Extra functions

Pymodbus: Modbus Protocol Implementation.

Released under the BSD license

class pymodbus.ExceptionResponse(function_code, exception_code=None, **kwargs)

Bases: ModbusResponse

Base class for a modbus exception PDU.

ExceptionOffset = 128
decode(data)

Decode a modbus exception response.

Parameters:

data – The packet data to decode

encode()

Encode a modbus exception response.

Returns:

The encoded exception packet

class pymodbus.Framer(value, names=None, *, module=None, qualname=None, type=None, start=1, boundary=None)

Bases: str, Enum

These represent the different framers.

ASCII = 'ascii'
RTU = 'rtu'
SOCKET = 'socket'
TLS = 'tls'
exception pymodbus.ModbusException(string)

Bases: Exception

Base modbus exception.

isError()

Error

pymodbus.pymodbus_apply_logging_config(level: str | int = 10, log_file_name: str | None = None)

Apply basic logging configuration used by default by Pymodbus maintainers.

Parameters:
  • level – (optional) set log level, if not set it is inherited.

  • log_file_name – (optional) log additional to file

Please call this function to format logging appropriately when opening issues.

Bit Reading Request/Response messages.

class pymodbus.bit_read_message.ReadBitsResponseBase(values, slave=0, **kwargs)

Bases: ModbusResponse

Base class for Messages responding to bit-reading values.

The requested bits can be found in the .bits list.

bits

A list of booleans representing bit values

decode(data)

Decode response pdu.

Parameters:

data – The packet data to decode

encode()

Encode response pdu.

Returns:

The encoded packet message

getBit(address)

Get the specified bit’s value.

Parameters:

address – The bit to query

Returns:

The value of the requested bit

resetBit(address)

Set the specified bit to 0.

Parameters:

address – The bit to reset

setBit(address, value=1)

Set the specified bit.

Parameters:
  • address – The bit to set

  • value – The value to set the bit to

class pymodbus.bit_read_message.ReadCoilsRequest(address=None, count=None, slave=0, **kwargs)

Bases: ReadBitsRequestBase

This function code is used to read from 1 to 2000(0x7d0) contiguous status of coils in a remote device.

The Request PDU specifies the starting address, ie the address of the first coil specified, and the number of coils. In the PDU Coils are addressed starting at zero. Therefore coils numbered 1-16 are addressed as 0-15.

execute(context)

Run a read coils request against a datastore.

Before running the request, we make sure that the request is in the max valid range (0x001-0x7d0). Next we make sure that the request is valid against the current datastore.

Parameters:

context – The datastore to request from

Returns:

An initialized ReadCoilsResponse, or an ExceptionResponse if an error occurred

function_code = 1
function_code_name = 'read_coils'
class pymodbus.bit_read_message.ReadCoilsResponse(values=None, slave=0, **kwargs)

Bases: ReadBitsResponseBase

The coils in the response message are packed as one coil per bit of the data field.

Status is indicated as 1= ON and 0= OFF. The LSB of the first data byte contains the output addressed in the query. The other coils follow toward the high order end of this byte, and from low order to high order in subsequent bytes.

If the returned output quantity is not a multiple of eight, the remaining bits in the final data byte will be padded with zeros (toward the high order end of the byte). The Byte Count field specifies the quantity of complete bytes of data.

The requested coils can be found in boolean form in the .bits list.

function_code = 1
class pymodbus.bit_read_message.ReadDiscreteInputsRequest(address=None, count=None, slave=0, **kwargs)

Bases: ReadBitsRequestBase

This function code is used to read from 1 to 2000(0x7d0).

Contiguous status of discrete inputs in a remote device. The Request PDU specifies the starting address, ie the address of the first input specified, and the number of inputs. In the PDU Discrete Inputs are addressed starting at zero. Therefore Discrete inputs numbered 1-16 are addressed as 0-15.

execute(context)

Run a read discrete input request against a datastore.

Before running the request, we make sure that the request is in the max valid range (0x001-0x7d0). Next we make sure that the request is valid against the current datastore.

Parameters:

context – The datastore to request from

Returns:

An initialized ReadDiscreteInputsResponse, or an ExceptionResponse if an error occurred

function_code = 2
function_code_name = 'read_discrete_input'
class pymodbus.bit_read_message.ReadDiscreteInputsResponse(values=None, slave=0, **kwargs)

Bases: ReadBitsResponseBase

The discrete inputs in the response message are packed as one input per bit of the data field.

Status is indicated as 1= ON; 0= OFF. The LSB of the first data byte contains the input addressed in the query. The other inputs follow toward the high order end of this byte, and from low order to high order in subsequent bytes.

If the returned input quantity is not a multiple of eight, the remaining bits in the final data byte will be padded with zeros (toward the high order end of the byte). The Byte Count field specifies the quantity of complete bytes of data.

The requested coils can be found in boolean form in the .bits list.

function_code = 2

Bit Writing Request/Response.

TODO write mask request/response

class pymodbus.bit_write_message.WriteMultipleCoilsRequest(address=None, values=None, slave=None, **kwargs)

Bases: ModbusRequest

This function code is used to forcea sequence of coils.

To either ON or OFF in a remote device. The Request PDU specifies the coil references to be forced. Coils are addressed starting at zero. Therefore coil numbered 1 is addressed as 0.

The requested ON/OFF states are specified by contents of the request data field. A logical “1” in a bit position of the field requests the corresponding output to be ON. A logical “0” requests it to be OFF.”

decode(data)

Decode a write coils request.

Parameters:

data – The packet data to decode

encode()

Encode write coils request.

Returns:

The byte encoded message

execute(context)

Run a write coils request against a datastore.

Parameters:

context – The datastore to request from

Returns:

The populated response or exception message

function_code = 15
function_code_name = 'write_coils'
get_response_pdu_size()

Get response pdu size.

Func_code (1 byte) + Output Address (2 byte) + Quantity of Outputs (2 Bytes) :return:

class pymodbus.bit_write_message.WriteMultipleCoilsResponse(address=None, count=None, **kwargs)

Bases: ModbusResponse

The normal response returns the function code.

Starting address, and quantity of coils forced.

decode(data)

Decode a write coils response.

Parameters:

data – The packet data to decode

encode()

Encode write coils response.

Returns:

The byte encoded message

function_code = 15
class pymodbus.bit_write_message.WriteSingleCoilRequest(address=None, value=None, slave=None, **kwargs)

Bases: ModbusRequest

This function code is used to write a single output to either ON or OFF in a remote device.

The requested ON/OFF state is specified by a constant in the request data field. A value of FF 00 hex requests the output to be ON. A value of 00 00 requests it to be OFF. All other values are illegal and will not affect the output.

The Request PDU specifies the address of the coil to be forced. Coils are addressed starting at zero. Therefore coil numbered 1 is addressed as 0. The requested ON/OFF state is specified by a constant in the Coil Value field. A value of 0XFF00 requests the coil to be ON. A value of 0X0000 requests the coil to be off. All other values are illegal and will not affect the coil.

decode(data)

Decode a write coil request.

Parameters:

data – The packet data to decode

encode()

Encode write coil request.

Returns:

The byte encoded message

execute(context)

Run a write coil request against a datastore.

Parameters:

context – The datastore to request from

Returns:

The populated response or exception message

function_code = 5
function_code_name = 'write_coil'
get_response_pdu_size()

Get response pdu size.

Func_code (1 byte) + Output Address (2 byte) + Output Value (2 Bytes) :return:

class pymodbus.bit_write_message.WriteSingleCoilResponse(address=None, value=None, **kwargs)

Bases: ModbusResponse

The normal response is an echo of the request.

Returned after the coil state has been written.

decode(data)

Decode a write coil response.

Parameters:

data – The packet data to decode

encode()

Encode write coil response.

Returns:

The byte encoded message

function_code = 5

Modbus Device Controller.

These are the device management handlers. They should be maintained in the server context and the various methods should be inserted in the correct locations.

class pymodbus.device.DeviceInformationFactory

Bases: object

This is a helper factory.

That really just hides some of the complexity of processing the device information requests (function code 0x2b 0x0e).

classmethod get(control, read_code=DeviceInformation.BASIC, object_id=0)

Get the requested device data from the system.

Parameters:
  • control – The control block to pull data from

  • read_code – The read code to process

  • object_id – The specific object_id to read

Returns:

The requested data (id, length, value)

class pymodbus.device.ModbusDeviceIdentification(info=None, info_name=None)

Bases: object

This is used to supply the device identification.

For the readDeviceIdentification function

For more information read section 6.21 of the modbus application protocol.

property MajorMinorRevision
property ModelName
property ProductCode
property ProductName
property UserApplicationName
property VendorName
property VendorUrl
summary()

Return a summary of the main items.

Returns:

An dictionary of the main items

update(value)

Update the values of this identity.

using another identify as the value

Parameters:

value – The value to copy values from

class pymodbus.device.ModbusPlusStatistics

Bases: object

This is used to maintain the current modbus plus statistics count.

As of right now this is simply a stub to complete the modbus implementation. For more information, see the modbus implementation guide page 87.

encode()

Return a summary of the modbus plus statistics.

Returns:

54 16-bit words representing the status

reset()

Clear all of the modbus plus statistics.

summary()

Return a summary of the modbus plus statistics.

Returns:

54 16-bit words representing the status

Diagnostic Record Read/Write.

These need to be tied into a the current server context or linked to the appropriate data

class pymodbus.diag_message.ChangeAsciiInputDelimiterRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Change ascii input delimiter.

The character “CHAR” passed in the request data field becomes the end of message delimiter for future messages (replacing the default LF character). This function is useful in cases of a Line Feed is not required at the end of ASCII messages.

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 3
class pymodbus.diag_message.ChangeAsciiInputDelimiterResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Change ascii input delimiter.

The character “CHAR” passed in the request data field becomes the end of message delimiter for future messages (replacing the default LF character). This function is useful in cases of a Line Feed is not required at the end of ASCII messages.

sub_function_code = 3
class pymodbus.diag_message.ClearCountersRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Clear ll counters and the diagnostic register.

Also, counters are cleared upon power-up

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 10
class pymodbus.diag_message.ClearCountersResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Clear ll counters and the diagnostic register.

Also, counters are cleared upon power-up

sub_function_code = 10
class pymodbus.diag_message.ClearOverrunCountRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Clear the overrun error counter and reset the error flag.

An error flag should be cleared, but nothing else in the specification mentions is, so it is ignored.

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 20
class pymodbus.diag_message.ClearOverrunCountResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Clear the overrun error counter and reset the error flag.

sub_function_code = 20
class pymodbus.diag_message.DiagnosticStatusRequest(**kwargs)

Bases: ModbusRequest

This is a base class for all of the diagnostic request functions.

decode(data)

Decode a diagnostic request.

Parameters:

data – The data to decode into the function code

encode()

Encode a diagnostic response.

we encode the data set in self.message

Returns:

The encoded packet

function_code = 8
function_code_name = 'diagnostic_status'
get_response_pdu_size()

Get response pdu size.

Func_code (1 byte) + Sub function code (2 byte) + Data (2 * N bytes) :return:

class pymodbus.diag_message.DiagnosticStatusResponse(**kwargs)

Bases: ModbusResponse

Diagnostic status.

This is a base class for all of the diagnostic response functions

It works by performing all of the encoding and decoding of variable data and lets the higher classes define what extra data to append and how to execute a request

decode(data)

Decode diagnostic response.

Parameters:

data – The data to decode into the function code

encode()

Encode diagnostic response.

we encode the data set in self.message

Returns:

The encoded packet

function_code = 8
class pymodbus.diag_message.ForceListenOnlyModeRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Forces the addressed remote device to its Listen Only Mode for MODBUS communications.

This isolates it from the other devices on the network, allowing them to continue communicating without interruption from the addressed remote device. No response is returned.

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 4
class pymodbus.diag_message.ForceListenOnlyModeResponse(**kwargs)

Bases: DiagnosticStatusResponse

Forces the addressed remote device to its Listen Only Mode for MODBUS communications.

This isolates it from the other devices on the network, allowing them to continue communicating without interruption from the addressed remote device. No response is returned.

This does not send a response

should_respond = False
sub_function_code = 4
class pymodbus.diag_message.GetClearModbusPlusRequest(slave=None, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Get/Clear modbus plus request.

In addition to the Function code (08) and Subfunction code (00 15 hex) in the query, a two-byte Operation field is used to specify either a “Get Statistics” or a “Clear Statistics” operation. The two operations are exclusive - the “Get” operation cannot clear the statistics, and the “Clear” operation does not return statistics prior to clearing them. Statistics are also cleared on power-up of the slave device.

encode()

Encode a diagnostic response.

we encode the data set in self.message

Returns:

The encoded packet

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

get_response_pdu_size()

Return a series of 54 16-bit words (108 bytes) in the data field of the response.

This function differs from the usual two-byte length of the data field. The data contains the statistics for the Modbus Plus peer processor in the slave device. Func_code (1 byte) + Sub function code (2 byte) + Operation (2 byte) + Data (108 bytes) :return:

sub_function_code = 21
class pymodbus.diag_message.GetClearModbusPlusResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Return a series of 54 16-bit words (108 bytes) in the data field of the response.

This function differs from the usual two-byte length of the data field. The data contains the statistics for the Modbus Plus peer processor in the slave device.

sub_function_code = 21
class pymodbus.diag_message.RestartCommunicationsOptionRequest(toggle=False, slave=None, **kwargs)

Bases: DiagnosticStatusRequest

Restart communication.

The remote device serial line port must be initialized and restarted, and all of its communications event counters are cleared. If the port is currently in Listen Only Mode, no response is returned. This function is the only one that brings the port out of Listen Only Mode. If the port is not currently in Listen Only Mode, a normal response is returned. This occurs before the restart is executed.

execute(*_args)

Clear event log and restart.

Returns:

The initialized response message

sub_function_code = 1
class pymodbus.diag_message.RestartCommunicationsOptionResponse(toggle=False, **kwargs)

Bases: DiagnosticStatusResponse

Restart Communication.

The remote device serial line port must be initialized and restarted, and all of its communications event counters are cleared. If the port is currently in Listen Only Mode, no response is returned. This function is the only one that brings the port out of Listen Only Mode. If the port is not currently in Listen Only Mode, a normal response is returned. This occurs before the restart is executed.

sub_function_code = 1
class pymodbus.diag_message.ReturnBusCommunicationErrorCountRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Return bus comm. count.

The response data field returns the quantity of CRC errors encountered by the remote device since its last restart, clear counter operation, or power-up

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 12
class pymodbus.diag_message.ReturnBusCommunicationErrorCountResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Return bus comm. error.

The response data field returns the quantity of CRC errors encountered by the remote device since its last restart, clear counter operation, or power-up

sub_function_code = 12
class pymodbus.diag_message.ReturnBusExceptionErrorCountRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Return bus exception.

The response data field returns the quantity of modbus exception responses returned by the remote device since its last restart, clear counters operation, or power-up

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 13
class pymodbus.diag_message.ReturnBusExceptionErrorCountResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Return bus exception.

The response data field returns the quantity of modbus exception responses returned by the remote device since its last restart, clear counters operation, or power-up

sub_function_code = 13
class pymodbus.diag_message.ReturnBusMessageCountRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Return bus message count.

The response data field returns the quantity of messages that the remote device has detected on the communications systems since its last restart, clear counters operation, or power-up

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 11
class pymodbus.diag_message.ReturnBusMessageCountResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Return bus message count.

The response data field returns the quantity of messages that the remote device has detected on the communications systems since its last restart, clear counters operation, or power-up

sub_function_code = 11
class pymodbus.diag_message.ReturnDiagnosticRegisterRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

The contents of the remote device’s 16-bit diagnostic register are returned in the response.

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 2
class pymodbus.diag_message.ReturnDiagnosticRegisterResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Return diagnostic register.

The contents of the remote device’s 16-bit diagnostic register are returned in the response

sub_function_code = 2
class pymodbus.diag_message.ReturnIopOverrunCountRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Return IopOverrun.

An IOP overrun is caused by data characters arriving at the port faster than they can be stored, or by the loss of a character due to a hardware malfunction. This function is specific to the 884.

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 19
class pymodbus.diag_message.ReturnIopOverrunCountResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Return Iop overrun count.

The response data field returns the quantity of messages addressed to the slave that it could not handle due to an 884 IOP overrun condition, since its last restart, clear counters operation, or power-up.

sub_function_code = 19
class pymodbus.diag_message.ReturnQueryDataRequest(message=b'\x00\x00', slave=None, **kwargs)

Bases: DiagnosticStatusRequest

Return query data.

The data passed in the request data field is to be returned (looped back) in the response. The entire response message should be identical to the request.

execute(*_args)

Execute the loopback request (builds the response).

Returns:

The populated loopback response message

sub_function_code = 0
class pymodbus.diag_message.ReturnQueryDataResponse(message=b'\x00\x00', **kwargs)

Bases: DiagnosticStatusResponse

Return query data.

The data passed in the request data field is to be returned (looped back) in the response. The entire response message should be identical to the request.

sub_function_code = 0
class pymodbus.diag_message.ReturnSlaveBusCharacterOverrunCountRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Return slave character overrun.

The response data field returns the quantity of messages addressed to the remote device that it could not handle due to a character overrun condition, since its last restart, clear counters operation, or power-up. A character overrun is caused by data characters arriving at the port faster than they can be stored, or by the loss of a character due to a hardware malfunction.

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 18
class pymodbus.diag_message.ReturnSlaveBusCharacterOverrunCountResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Return the quantity of messages addressed to the remote device unhandled due to a character overrun.

Since its last restart, clear counters operation, or power-up. A character overrun is caused by data characters arriving at the port faster than they can be stored, or by the loss of a character due to a hardware malfunction.

sub_function_code = 18
class pymodbus.diag_message.ReturnSlaveBusyCountRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Return slave busy count.

The response data field returns the quantity of messages addressed to the remote device for which it returned a Slave Device Busy exception response, since its last restart, clear counters operation, or power-up.

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 17
class pymodbus.diag_message.ReturnSlaveBusyCountResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Return slave busy count.

The response data field returns the quantity of messages addressed to the remote device for which it returned a Slave Device Busy exception response, since its last restart, clear counters operation, or power-up.

sub_function_code = 17
class pymodbus.diag_message.ReturnSlaveMessageCountRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Return slave message count.

The response data field returns the quantity of messages addressed to the remote device, or broadcast, that the remote device has processed since its last restart, clear counters operation, or power-up

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 14
class pymodbus.diag_message.ReturnSlaveMessageCountResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Return slave message count.

The response data field returns the quantity of messages addressed to the remote device, or broadcast, that the remote device has processed since its last restart, clear counters operation, or power-up

sub_function_code = 14
class pymodbus.diag_message.ReturnSlaveNAKCountRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Return slave NAK count.

The response data field returns the quantity of messages addressed to the remote device for which it returned a Negative Acknowledge (NAK) exception response, since its last restart, clear counters operation, or power-up. Exception responses are described and listed in section 7 .

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 16
class pymodbus.diag_message.ReturnSlaveNAKCountResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Return slave NAK.

The response data field returns the quantity of messages addressed to the remote device for which it returned a Negative Acknowledge (NAK) exception response, since its last restart, clear counters operation, or power-up. Exception responses are described and listed in section 7.

sub_function_code = 16
class pymodbus.diag_message.ReturnSlaveNoResponseCountRequest(data=0, **kwargs)

Bases: DiagnosticStatusSimpleRequest

Return slave no response.

The response data field returns the quantity of messages addressed to the remote device, or broadcast, that the remote device has processed since its last restart, clear counters operation, or power-up

execute(*args)

Execute the diagnostic request on the given device.

Returns:

The initialized response message

sub_function_code = 15
class pymodbus.diag_message.ReturnSlaveNoResponseCountResponse(data=0, **kwargs)

Bases: DiagnosticStatusSimpleResponse

Return slave no response.

The response data field returns the quantity of messages addressed to the remote device, or broadcast, that the remote device has processed since its last restart, clear counters operation, or power-up

sub_function_code = 15

Modbus Remote Events.

An event byte returned by the Get Communications Event Log function can be any one of four types. The type is defined by bit 7 (the high-order bit) in each byte. It may be further defined by bit 6.

class pymodbus.events.CommunicationRestartEvent

Bases: ModbusEvent

Restart remote device Initiated Communication.

The remote device stores this type of event byte when its communications port is restarted. The remote device can be restarted by the Diagnostics function (code 08), with sub-function Restart Communications Option (code 00 01).

That function also places the remote device into a “Continue on Error” or “Stop on Error” mode. If the remote device is placed into “Continue on Error” mode, the event byte is added to the existing event log. If the remote device is placed into “Stop on Error” mode, the byte is added to the log and the rest of the log is cleared to zeros.

The event is defined by a content of zero.

decode(event)

Decode the event message to its status bits.

Parameters:

event – The event to decode

Raises:

ParameterException

encode()

Encode the status bits to an event message.

Returns:

The encoded event message

value = 0
class pymodbus.events.EnteredListenModeEvent

Bases: ModbusEvent

Enter Remote device Listen Only Mode.

The remote device stores this type of event byte when it enters the Listen Only Mode. The event is defined by a content of 04 hex.

decode(event)

Decode the event message to its status bits.

Parameters:

event – The event to decode

Raises:

ParameterException

encode()

Encode the status bits to an event message.

Returns:

The encoded event message

value = 4
class pymodbus.events.ModbusEvent

Bases: object

Define modbus events.

decode(event)

Decode the event message to its status bits.

Parameters:

event – The event to decode

Raises:

NotImplementedException

encode()

Encode the status bits to an event message.

Raises:

NotImplementedException

class pymodbus.events.RemoteReceiveEvent(**kwargs)

Bases: ModbusEvent

Remote device MODBUS Receive Event.

The remote device stores this type of event byte when a query message is received. It is stored before the remote device processes the message. This event is defined by bit 7 set to logic “1”. The other bits will be set to a logic “1” if the corresponding condition is TRUE. The bit layout is:

Bit Contents
----------------------------------
0   Not Used
2   Not Used
3   Not Used
4   Character Overrun
5   Currently in Listen Only Mode
6   Broadcast Receive
7   1
decode(event: bytes) None

Decode the event message to its status bits.

Parameters:

event – The event to decode

encode() bytes

Encode the status bits to an event message.

Returns:

The encoded event message

class pymodbus.events.RemoteSendEvent(**kwargs)

Bases: ModbusEvent

Remote device MODBUS Send Event.

The remote device stores this type of event byte when it finishes processing a request message. It is stored if the remote device returned a normal or exception response, or no response.

This event is defined by bit 7 set to a logic “0”, with bit 6 set to a “1”. The other bits will be set to a logic “1” if the corresponding condition is TRUE. The bit layout is:

Bit Contents
-----------------------------------------------------------
0   Read Exception Sent (Exception Codes 1-3)
1   Slave Abort Exception Sent (Exception Code 4)
2   Slave Busy Exception Sent (Exception Codes 5-6)
3   Slave Program NAK Exception Sent (Exception Code 7)
4   Write Timeout Error Occurred
5   Currently in Listen Only Mode
6   1
7   0
decode(event)

Decode the event message to its status bits.

Parameters:

event – The event to decode

encode()

Encode the status bits to an event message.

Returns:

The encoded event message

Pymodbus Exceptions.

Custom exceptions to be used in the Modbus code.

exception pymodbus.exceptions.ConnectionException(string='')

Bases: ModbusException

Error resulting from a bad connection.

exception pymodbus.exceptions.InvalidMessageReceivedException(string='')

Bases: ModbusException

Error resulting from invalid response received or decoded.

exception pymodbus.exceptions.MessageRegisterException(string='')

Bases: ModbusException

Error resulting from failing to register a custom message request/response.

exception pymodbus.exceptions.ModbusIOException(string='', function_code=None)

Bases: ModbusException

Error resulting from data i/o.

exception pymodbus.exceptions.NoSuchSlaveException(string='')

Bases: ModbusException

Error resulting from making a request to a slave that does not exist.

exception pymodbus.exceptions.NotImplementedException(string='')

Bases: ModbusException

Error resulting from not implemented function.

exception pymodbus.exceptions.ParameterException(string='')

Bases: ModbusException

Error resulting from invalid parameter.

Modbus Request/Response Decoder Factories.

The following factories make it easy to decode request/response messages. To add a new request/response pair to be decodeable by the library, simply add them to the respective function lookup table (order doesn’t matter, but it does help keep things organized).

Regardless of how many functions are added to the lookup, O(1) behavior is kept as a result of a pre-computed lookup dictionary.

class pymodbus.factory.ClientDecoder

Bases: object

Response Message Factory (Client).

To add more implemented functions, simply add them to the list

decode(message)

Decode a response packet.

Parameters:

message – The raw packet to decode

Returns:

The decoded modbus message or None if error

function_table = [<class 'pymodbus.register_read_message.ReadHoldingRegistersResponse'>, <class 'pymodbus.bit_read_message.ReadDiscreteInputsResponse'>, <class 'pymodbus.register_read_message.ReadInputRegistersResponse'>, <class 'pymodbus.bit_read_message.ReadCoilsResponse'>, <class 'pymodbus.bit_write_message.WriteMultipleCoilsResponse'>, <class 'pymodbus.register_write_message.WriteMultipleRegistersResponse'>, <class 'pymodbus.register_write_message.WriteSingleRegisterResponse'>, <class 'pymodbus.bit_write_message.WriteSingleCoilResponse'>, <class 'pymodbus.register_read_message.ReadWriteMultipleRegistersResponse'>, <class 'pymodbus.diag_message.DiagnosticStatusResponse'>, <class 'pymodbus.other_message.ReadExceptionStatusResponse'>, <class 'pymodbus.other_message.GetCommEventCounterResponse'>, <class 'pymodbus.other_message.GetCommEventLogResponse'>, <class 'pymodbus.other_message.ReportSlaveIdResponse'>, <class 'pymodbus.file_message.ReadFileRecordResponse'>, <class 'pymodbus.file_message.WriteFileRecordResponse'>, <class 'pymodbus.register_write_message.MaskWriteRegisterResponse'>, <class 'pymodbus.file_message.ReadFifoQueueResponse'>, <class 'pymodbus.mei_message.ReadDeviceInformationResponse'>]
lookupPduClass(function_code)

Use function_code to determine the class of the PDU.

Parameters:

function_code – The function code specified in a frame.

Returns:

The class of the PDU that has a matching function_code.

register(function)

Register a function and sub function class with the decoder.

class pymodbus.factory.ServerDecoder

Bases: object

Request Message Factory (Server).

To add more implemented functions, simply add them to the list

decode(message)

Decode a request packet.

Parameters:

message – The raw modbus request packet

Returns:

The decoded modbus message or None if error

classmethod getFCdict() dict[int, Callable]

Build function code - class list.

lookupPduClass(function_code)

Use function_code to determine the class of the PDU.

Parameters:

function_code – The function code specified in a frame.

Returns:

The class of the PDU that has a matching function_code.

register(function)

Register a function and sub function class with the decoder.

Parameters:

function – Custom function class to register

Raises:

MessageRegisterException

File Record Read/Write Messages.

Currently none of these messages are implemented

class pymodbus.file_message.FileRecord(**kwargs)

Bases: object

Represents a file record and its relevant data.

class pymodbus.file_message.ReadFifoQueueRequest(address=0, **kwargs)

Bases: ModbusRequest

Read fifo queue request.

This function code allows to read the contents of a First-In-First-Out (FIFO) queue of register in a remote device. The function returns a count of the registers in the queue, followed by the queued data. Up to 32 registers can be read: the count, plus up to 31 queued data registers.

The queue count register is returned first, followed by the queued data registers. The function reads the queue contents, but does not clear them.

decode(data)

Decode the incoming request.

Parameters:

data – The data to decode into the address

encode()

Encode the request packet.

Returns:

The byte encoded packet

execute(_context)

Run a read exception status request against the store.

Returns:

The populated response

function_code = 24
function_code_name = 'read_fifo_queue'
class pymodbus.file_message.ReadFifoQueueResponse(values=None, **kwargs)

Bases: ModbusResponse

Read Fifo queue response.

In a normal response, the byte count shows the quantity of bytes to follow, including the queue count bytes and value register bytes (but not including the error check field). The queue count is the quantity of data registers in the queue (not including the count register).

If the queue count exceeds 31, an exception response is returned with an error code of 03 (Illegal Data Value).

classmethod calculateRtuFrameSize(buffer)

Calculate the size of the message.

Parameters:

buffer – A buffer containing the data that have been received.

Returns:

The number of bytes in the response.

decode(data)

Decode a the response.

Parameters:

data – The packet data to decode

encode()

Encode the response.

Returns:

The byte encoded message

function_code = 24
class pymodbus.file_message.ReadFileRecordRequest(records=None, **kwargs)

Bases: ModbusRequest

Read file record request.

This function code is used to perform a file record read. All request data lengths are provided in terms of number of bytes and all record lengths are provided in terms of registers.

A file is an organization of records. Each file contains 10000 records, addressed 0000 to 9999 decimal or 0x0000 to 0x270f. For example, record 12 is addressed as 12. The function can read multiple groups of references. The groups can be separating (non-contiguous), but the references within each group must be sequential. Each group is defined in a separate “sub-request” field that contains seven bytes:

The reference type: 1 byte (must be 0x06)
The file number: 2 bytes
The starting record number within the file: 2 bytes
The length of the record to be read: 2 bytes

The quantity of registers to be read, combined with all other fields in the expected response, must not exceed the allowable length of the MODBUS PDU: 235 bytes.

decode(data)

Decode the incoming request.

Parameters:

data – The data to decode into the address

encode()

Encode the request packet.

Returns:

The byte encoded packet

execute(_context)

Run a read exception status request against the store.

Returns:

The populated response

function_code = 20
function_code_name = 'read_file_record'
class pymodbus.file_message.ReadFileRecordResponse(records=None, **kwargs)

Bases: ModbusResponse

Read file record response.

The normal response is a series of “sub-responses,” one for each “sub-request.” The byte count field is the total combined count of bytes in all “sub-responses.” In addition, each “sub-response” contains a field that shows its own byte count.

decode(data)

Decode the response.

Parameters:

data – The packet data to decode

encode()

Encode the response.

Returns:

The byte encoded message

function_code = 20
class pymodbus.file_message.WriteFileRecordRequest(records=None, **kwargs)

Bases: ModbusRequest

Write file record request.

This function code is used to perform a file record write. All request data lengths are provided in terms of number of bytes and all record lengths are provided in terms of the number of 16 bit words.

decode(data)

Decode the incoming request.

Parameters:

data – The data to decode into the address

encode()

Encode the request packet.

Returns:

The byte encoded packet

execute(_context)

Run the write file record request against the context.

Returns:

The populated response

function_code = 21
function_code_name = 'write_file_record'
class pymodbus.file_message.WriteFileRecordResponse(records=None, **kwargs)

Bases: ModbusResponse

The normal response is an echo of the request.

decode(data)

Decode the incoming request.

Parameters:

data – The data to decode into the address

encode()

Encode the response.

Returns:

The byte encoded message

function_code = 21

Encapsulated Interface (MEI) Transport Messages.

class pymodbus.mei_message.ReadDeviceInformationRequest(read_code=None, object_id=0, **kwargs)

Bases: ModbusRequest

Read device information.

This function code allows reading the identification and additional information relative to the physical and functional description of a remote device, only.

The Read Device Identification interface is modeled as an address space composed of a set of addressable data elements. The data elements are called objects and an object Id identifies them.

decode(data)

Decode data part of the message.

Parameters:

data – The incoming data

encode()

Encode the request packet.

Returns:

The byte encoded packet

execute(_context)

Run a read exception status request against the store.

Returns:

The populated response

function_code = 43
function_code_name = 'read_device_information'
sub_function_code = 14
class pymodbus.mei_message.ReadDeviceInformationResponse(read_code=None, information=None, **kwargs)

Bases: ModbusResponse

Read device information response.

classmethod calculateRtuFrameSize(buffer)

Calculate the size of the message.

Parameters:

buffer – A buffer containing the data that have been received.

Returns:

The number of bytes in the response.

decode(data)

Decode a the response.

Parameters:

data – The packet data to decode

encode()

Encode the response.

Returns:

The byte encoded message

function_code = 43
sub_function_code = 14

Diagnostic record read/write.

Currently not all implemented

class pymodbus.other_message.GetCommEventCounterRequest(**kwargs)

Bases: ModbusRequest

This function code is used to get a status word.

And an event count from the remote device’s communication event counter.

By fetching the current count before and after a series of messages, a client can determine whether the messages were handled normally by the remote device.

The device’s event counter is incremented once for each successful message completion. It is not incremented for exception responses, poll commands, or fetch event counter commands.

The event counter can be reset by means of the Diagnostics function (code 08), with a subfunction of Restart Communications Option (code 00 01) or Clear Counters and Diagnostic Register (code 00 0A).

decode(data)

Decode data part of the message.

Parameters:

data – The incoming data

encode()

Encode the message.

execute(_context=None)

Run a read exception status request against the store.

Returns:

The populated response

function_code = 11
function_code_name = 'get_event_counter'
class pymodbus.other_message.GetCommEventCounterResponse(count=0, **kwargs)

Bases: ModbusResponse

Get comm event counter response.

The normal response contains a two-byte status word, and a two-byte event count. The status word will be all ones (FF FF hex) if a previously-issued program command is still being processed by the remote device (a busy condition exists). Otherwise, the status word will be all zeros.

decode(data)

Decode a the response.

Parameters:

data – The packet data to decode

encode()

Encode the response.

Returns:

The byte encoded message

function_code = 11
class pymodbus.other_message.GetCommEventLogRequest(**kwargs)

Bases: ModbusRequest

This function code is used to get a status word.

Event count, message count, and a field of event bytes from the remote device.

The status word and event counts are identical to that returned by the Get Communications Event Counter function (11, 0B hex).

The message counter contains the quantity of messages processed by the remote device since its last restart, clear counters operation, or power-up. This count is identical to that returned by the Diagnostic function (code 08), sub-function Return Bus Message Count (code 11, 0B hex).

The event bytes field contains 0-64 bytes, with each byte corresponding to the status of one MODBUS send or receive operation for the remote device. The remote device enters the events into the field in chronological order. Byte 0 is the most recent event. Each new byte flushes the oldest byte from the field.

decode(data)

Decode data part of the message.

Parameters:

data – The incoming data

encode()

Encode the message.

execute(_context=None)

Run a read exception status request against the store.

Returns:

The populated response

function_code = 12
function_code_name = 'get_event_log'
class pymodbus.other_message.GetCommEventLogResponse(**kwargs)

Bases: ModbusResponse

Get Comm event log response.

The normal response contains a two-byte status word field, a two-byte event count field, a two-byte message count field, and a field containing 0-64 bytes of events. A byte count field defines the total length of the data in these four field

decode(data)

Decode a the response.

Parameters:

data – The packet data to decode

encode()

Encode the response.

Returns:

The byte encoded message

function_code = 12
class pymodbus.other_message.ReadExceptionStatusRequest(slave=None, **kwargs)

Bases: ModbusRequest

This function code is used to read the contents of eight Exception Status outputs in a remote device.

The function provides a simple method for accessing this information, because the Exception Output references are known (no output reference is needed in the function).

decode(data)

Decode data part of the message.

Parameters:

data – The incoming data

encode()

Encode the message.

execute(_context=None)

Run a read exception status request against the store.

Returns:

The populated response

function_code = 7
function_code_name = 'read_exception_status'
class pymodbus.other_message.ReadExceptionStatusResponse(status=0, **kwargs)

Bases: ModbusResponse

The normal response contains the status of the eight Exception Status outputs.

The outputs are packed into one data byte, with one bit per output. The status of the lowest output reference is contained in the least significant bit of the byte. The contents of the eight Exception Status outputs are device specific.

decode(data)

Decode a the response.

Parameters:

data – The packet data to decode

encode()

Encode the response.

Returns:

The byte encoded message

function_code = 7
class pymodbus.other_message.ReportSlaveIdRequest(slave=0, **kwargs)

Bases: ModbusRequest

This function code is used to read the description of the type.

The current status, and other information specific to a remote device.

decode(data)

Decode data part of the message.

Parameters:

data – The incoming data

encode()

Encode the message.

execute(context=None)

Run a report slave id request against the store.

Returns:

The populated response

function_code = 17
function_code_name = 'report_slave_id'
class pymodbus.other_message.ReportSlaveIdResponse(identifier=b'\x00', status=True, **kwargs)

Bases: ModbusResponse

Show response.

The data contents are specific to each type of device.

decode(data)

Decode a the response.

Since the identifier is device dependent, we just return the raw value that a user can decode to whatever it should be.

Parameters:

data – The packet data to decode

encode()

Encode the response.

Returns:

The byte encoded message

function_code = 17

Modbus Payload Builders.

A collection of utilities for building and decoding modbus messages payloads.

class pymodbus.payload.BinaryPayloadBuilder(payload=None, byteorder=Endian.LITTLE, wordorder=Endian.BIG, repack=False)

Bases: object

A utility that helps build payload messages to be written with the various modbus messages.

It really is just a simple wrapper around the struct module, however it saves time looking up the format strings. What follows is a simple example:

builder = BinaryPayloadBuilder(byteorder=Endian.Little)
builder.add_8bit_uint(1)
builder.add_16bit_uint(2)
payload = builder.build()
add_16bit_float(value: float) None

Add a 16 bit float to the buffer.

Parameters:

value – The value to add to the buffer

add_16bit_int(value: int) None

Add a 16 bit signed int to the buffer.

Parameters:

value – The value to add to the buffer

add_16bit_uint(value: int) None

Add a 16 bit unsigned int to the buffer.

Parameters:

value – The value to add to the buffer

add_32bit_float(value: float) None

Add a 32 bit float to the buffer.

Parameters:

value – The value to add to the buffer

add_32bit_int(value: int) None

Add a 32 bit signed int to the buffer.

Parameters:

value – The value to add to the buffer

add_32bit_uint(value: int) None

Add a 32 bit unsigned int to the buffer.

Parameters:

value – The value to add to the buffer

add_64bit_float(value: float) None

Add a 64 bit float(double) to the buffer.

Parameters:

value – The value to add to the buffer

add_64bit_int(value: int) None

Add a 64 bit signed int to the buffer.

Parameters:

value – The value to add to the buffer

add_64bit_uint(value: int) None

Add a 64 bit unsigned int to the buffer.

Parameters:

value – The value to add to the buffer

add_8bit_int(value: int) None

Add a 8 bit signed int to the buffer.

Parameters:

value – The value to add to the buffer

add_8bit_uint(value: int) None

Add a 8 bit unsigned int to the buffer.

Parameters:

value – The value to add to the buffer

add_bits(values: list[bool]) None

Add a collection of bits to be encoded.

If these are less than a multiple of eight, they will be left padded with 0 bits to make it so.

Parameters:

values – The value to add to the buffer

add_string(value: str) None

Add a string to the buffer.

Parameters:

value – The value to add to the buffer

build() list[bytes]

Return the payload buffer as a list.

This list is two bytes per element and can thus be treated as a list of registers.

Returns:

The payload buffer as a list

encode() bytes

Get the payload buffer encoded in bytes.

reset() None

Reset the payload buffer.

to_coils() list[bool]

Convert the payload buffer into a coil layout that can be used as a context block.

Returns:

The coil layout to use as a block

to_registers()

Convert the payload buffer to register layout that can be used as a context block.

Returns:

The register layout to use as a block

class pymodbus.payload.BinaryPayloadDecoder(payload, byteorder=Endian.LITTLE, wordorder=Endian.BIG)

Bases: object

A utility that helps decode payload messages from a modbus response message.

It really is just a simple wrapper around the struct module, however it saves time looking up the format strings. What follows is a simple example:

decoder = BinaryPayloadDecoder(payload)
first   = decoder.decode_8bit_uint()
second  = decoder.decode_16bit_uint()
classmethod bit_chunks(coils, size=8)

Return bit chunks.

decode_16bit_float()

Decode a 16 bit float from the buffer.

decode_16bit_int()

Decode a 16 bit signed int from the buffer.

decode_16bit_uint()

Decode a 16 bit unsigned int from the buffer.

decode_32bit_float()

Decode a 32 bit float from the buffer.

decode_32bit_int()

Decode a 32 bit signed int from the buffer.

decode_32bit_uint()

Decode a 32 bit unsigned int from the buffer.

decode_64bit_float()

Decode a 64 bit float(double) from the buffer.

decode_64bit_int()

Decode a 64 bit signed int from the buffer.

decode_64bit_uint()

Decode a 64 bit unsigned int from the buffer.

decode_8bit_int()

Decode a 8 bit signed int from the buffer.

decode_8bit_uint()

Decode a 8 bit unsigned int from the buffer.

decode_bits(package_len=1)

Decode a byte worth of bits from the buffer.

decode_string(size=1)

Decode a string from the buffer.

Parameters:

size – The size of the string to decode

classmethod fromCoils(coils, byteorder=Endian.LITTLE, _wordorder=Endian.BIG)

Initialize a payload decoder with the result of reading of coils.

classmethod fromRegisters(registers, byteorder=Endian.LITTLE, wordorder=Endian.BIG)

Initialize a payload decoder.

With the result of reading a collection of registers from a modbus device.

The registers are treated as a list of 2 byte values. We have to do this because of how the data has already been decoded by the rest of the library.

Parameters:
  • registers – The register results to initialize with

  • byteorder – The Byte order of each word

  • wordorder – The endianness of the word (when wordcount is >= 2)

Returns:

An initialized PayloadDecoder

Raises:

ParameterException

reset()

Reset the decoder pointer back to the start.

skip_bytes(nbytes)

Skip n bytes in the buffer.

Parameters:

nbytes – The number of bytes to skip

Contains base classes for modbus request/response/error packets.

class pymodbus.pdu.ExceptionResponse(function_code, exception_code=None, **kwargs)

Bases: ModbusResponse

Base class for a modbus exception PDU.

ExceptionOffset = 128
decode(data)

Decode a modbus exception response.

Parameters:

data – The packet data to decode

encode()

Encode a modbus exception response.

Returns:

The encoded exception packet

class pymodbus.pdu.IllegalFunctionRequest(function_code, **kwargs)

Bases: ModbusRequest

Define the Modbus slave exception type “Illegal Function”.

This exception code is returned if the slave:

- does not implement the function code **or**
- is not in a state that allows it to process the function
ErrorCode = 1
decode(_data)

Decode so this failure will run correctly.

encode()

Decode so this failure will run correctly.

execute(_context)

Build an illegal function request error response.

Returns:

The error response packet

class pymodbus.pdu.ModbusExceptions

Bases: object

An enumeration of the valid modbus exceptions.

Acknowledge = 5
GatewayNoResponse = 11
GatewayPathUnavailable = 10
IllegalAddress = 2
IllegalFunction = 1
IllegalValue = 3
MemoryParityError = 8
NegativeAcknowledge = 7
SlaveBusy = 6
SlaveFailure = 4
classmethod decode(code)

Give an error code, translate it to a string error name.

Parameters:

code – The code number to translate

class pymodbus.pdu.ModbusRequest(slave=0, **kwargs)

Bases: ModbusPDU

Base class for a modbus request PDU.

doException(exception)

Build an error response based on the function.

Parameters:

exception – The exception to return

Raises:

An exception response

function_code = -1
class pymodbus.pdu.ModbusResponse(slave=0, **kwargs)

Bases: ModbusPDU

Base class for a modbus response PDU.

should_respond

A flag that indicates if this response returns a result back to the client issuing the request

_rtu_frame_size

Indicates the size of the modbus rtu response used for calculating how much to read.

function_code = 0
isError() bool

Check if the error is a success or failure.

should_respond = True

Register Reading Request/Response.

class pymodbus.register_read_message.ReadHoldingRegistersRequest(address=None, count=None, slave=0, **kwargs)

Bases: ReadRegistersRequestBase

Read holding registers.

This function code is used to read the contents of a contiguous block of holding registers in a remote device. The Request PDU specifies the starting register address and the number of registers. In the PDU Registers are addressed starting at zero. Therefore registers numbered 1-16 are addressed as 0-15.

execute(context)

Run a read holding request against a datastore.

Parameters:

context – The datastore to request from

Returns:

An initialized ReadHoldingRegistersResponse, or an ExceptionResponse if an error occurred

function_code = 3
function_code_name = 'read_holding_registers'
class pymodbus.register_read_message.ReadHoldingRegistersResponse(values=None, **kwargs)

Bases: ReadRegistersResponseBase

Read holding registers.

This function code is used to read the contents of a contiguous block of holding registers in a remote device. The Request PDU specifies the starting register address and the number of registers. In the PDU Registers are addressed starting at zero. Therefore registers numbered 1-16 are addressed as 0-15.

The requested registers can be found in the .registers list.

function_code = 3
class pymodbus.register_read_message.ReadInputRegistersRequest(address=None, count=None, slave=0, **kwargs)

Bases: ReadRegistersRequestBase

Read input registers.

This function code is used to read from 1 to approx. 125 contiguous input registers in a remote device. The Request PDU specifies the starting register address and the number of registers. In the PDU Registers are addressed starting at zero. Therefore input registers numbered 1-16 are addressed as 0-15.

execute(context)

Run a read input request against a datastore.

Parameters:

context – The datastore to request from

Returns:

An initialized ReadInputRegistersResponse, or an ExceptionResponse if an error occurred

function_code = 4
function_code_name = 'read_input_registers'
class pymodbus.register_read_message.ReadInputRegistersResponse(values=None, **kwargs)

Bases: ReadRegistersResponseBase

Read/write input registers.

This function code is used to read from 1 to approx. 125 contiguous input registers in a remote device. The Request PDU specifies the starting register address and the number of registers. In the PDU Registers are addressed starting at zero. Therefore input registers numbered 1-16 are addressed as 0-15.

The requested registers can be found in the .registers list.

function_code = 4
class pymodbus.register_read_message.ReadRegistersResponseBase(values, slave=0, **kwargs)

Bases: ModbusResponse

Base class for responding to a modbus register read.

The requested registers can be found in the .registers list.

decode(data)

Decode a register response packet.

Parameters:

data – The request to decode

encode()

Encode the response packet.

Returns:

The encoded packet

getRegister(index)

Get the requested register.

Parameters:

index – The indexed register to retrieve

Returns:

The request register

registers

A list of register values

class pymodbus.register_read_message.ReadWriteMultipleRegistersRequest(**kwargs)

Bases: ModbusRequest

Read/write multiple registers.

This function code performs a combination of one read operation and one write operation in a single MODBUS transaction. The write operation is performed before the read.

Holding registers are addressed starting at zero. Therefore holding registers 1-16 are addressed in the PDU as 0-15.

The request specifies the starting address and number of holding registers to be read as well as the starting address, number of holding registers, and the data to be written. The byte count specifies the number of bytes to follow in the write data field.”

decode(data)

Decode the register request packet.

Parameters:

data – The request to decode

encode()

Encode the request packet.

Returns:

The encoded packet

execute(context)

Run a write single register request against a datastore.

Parameters:

context – The datastore to request from

Returns:

An initialized ReadWriteMultipleRegistersResponse, or an ExceptionResponse if an error occurred

function_code = 23
function_code_name = 'read_write_multiple_registers'
get_response_pdu_size()

Get response pdu size.

Func_code (1 byte) + Byte Count(1 byte) + 2 * Quantity of Coils (n Bytes) :return:

class pymodbus.register_read_message.ReadWriteMultipleRegistersResponse(values=None, **kwargs)

Bases: ModbusResponse

Read/write multiple registers.

The normal response contains the data from the group of registers that were read. The byte count field specifies the quantity of bytes to follow in the read data field.

The requested registers can be found in the .registers list.

decode(data)

Decode the register response packet.

Parameters:

data – The response to decode

encode()

Encode the response packet.

Returns:

The encoded packet

function_code = 23

Register Writing Request/Response Messages.

class pymodbus.register_write_message.MaskWriteRegisterRequest(address=0, and_mask=65535, or_mask=0, **kwargs)

Bases: ModbusRequest

This function code is used to modify the contents.

Of a specified holding register using a combination of an AND mask, an OR mask, and the register’s current contents. The function can be used to set or clear individual bits in the register.

decode(data)

Decode the incoming request.

Parameters:

data – The data to decode into the address

encode()

Encode the request packet.

Returns:

The byte encoded packet

execute(context)

Run a mask write register request against the store.

Parameters:

context – The datastore to request from

Returns:

The populated response

function_code = 22
function_code_name = 'mask_write_register'
class pymodbus.register_write_message.MaskWriteRegisterResponse(address=0, and_mask=65535, or_mask=0, **kwargs)

Bases: ModbusResponse

The normal response is an echo of the request.

The response is returned after the register has been written.

decode(data)

Decode a the response.

Parameters:

data – The packet data to decode

encode()

Encode the response.

Returns:

The byte encoded message

function_code = 22
class pymodbus.register_write_message.WriteMultipleRegistersRequest(address=None, values=None, slave=None, **kwargs)

Bases: ModbusRequest

This function code is used to write a block.

Of contiguous registers (1 to approx. 120 registers) in a remote device.

The requested written values are specified in the request data field. Data is packed as two bytes per register.

decode(data)

Decode a write single register packet packet request.

Parameters:

data – The request to decode

encode()

Encode a write single register packet packet request.

Returns:

The encoded packet

execute(context)

Run a write single register request against a datastore.

Parameters:

context – The datastore to request from

Returns:

An initialized response, exception message otherwise

function_code = 16
function_code_name = 'write_registers'
get_response_pdu_size()

Get response pdu size.

Func_code (1 byte) + Starting Address (2 byte) + Quantity of Registers (2 Bytes) :return:

class pymodbus.register_write_message.WriteMultipleRegistersResponse(address=None, count=None, **kwargs)

Bases: ModbusResponse

The normal response returns the function code.

Starting address, and quantity of registers written.

decode(data)

Decode a write single register packet packet request.

Parameters:

data – The request to decode

encode()

Encode a write single register packet packet request.

Returns:

The encoded packet

function_code = 16
class pymodbus.register_write_message.WriteSingleRegisterRequest(address=None, value=None, slave=None, **kwargs)

Bases: ModbusRequest

This function code is used to write a single holding register in a remote device.

The Request PDU specifies the address of the register to be written. Registers are addressed starting at zero. Therefore register numbered 1 is addressed as 0.

decode(data)

Decode a write single register packet packet request.

Parameters:

data – The request to decode

encode()

Encode a write single register packet packet request.

Returns:

The encoded packet

execute(context)

Run a write single register request against a datastore.

Parameters:

context – The datastore to request from

Returns:

An initialized response, exception message otherwise

function_code = 6
function_code_name = 'write_register'
get_response_pdu_size()

Get response pdu size.

Func_code (1 byte) + Register Address(2 byte) + Register Value (2 bytes) :return:

class pymodbus.register_write_message.WriteSingleRegisterResponse(address=None, value=None, **kwargs)

Bases: ModbusResponse

The normal response is an echo of the request.

Returned after the register contents have been written.

decode(data)

Decode a write single register packet packet request.

Parameters:

data – The request to decode

encode()

Encode a write single register packet packet request.

Returns:

The encoded packet

function_code = 6
get_response_pdu_size()

Get response pdu size.

Func_code (1 byte) + Starting Address (2 byte) + And_mask (2 Bytes) + OrMask (2 Bytes) :return:

Collection of transaction based abstractions.

class pymodbus.transaction.DictTransactionManager(client, **kwargs)

Bases: ModbusTransactionManager

Old alias for ModbusTransactionManager.

class pymodbus.transaction.ModbusAsciiFramer(decoder, client=None)

Bases: ModbusFramer

Modbus ASCII Frame Controller.

[ Start ][Address ][ Function ][ Data ][ LRC ][ End ]

1c 2c 2c Nc 2c 2c

  • data can be 0 - 2x252 chars

  • end is “\r\n” (Carriage return line feed), however the line feed character can be changed via a special command

  • start is “:”

This framer is used for serial transmission. Unlike the RTU protocol, the data in this framer is transferred in plain text ascii.

buildPacket(message)

Create a ready to send modbus packet.

Parameters:

message – The request/response to send

Returns:

The encoded packet

decode_data(data)

Decode data.

frameProcessIncomingPacket(single, callback, slave, _tid=None, **kwargs)

Process new packet pattern.

method = 'ascii'
class pymodbus.transaction.ModbusRtuFramer(decoder, client=None)

Bases: ModbusFramer

Modbus RTU Frame controller.

[ Start Wait ] [Address ][ Function Code] [ Data ][ CRC ][ End Wait ]

3.5 chars 1b 1b Nb 2b 3.5 chars

Wait refers to the amount of time required to transmit at least x many characters. In this case it is 3.5 characters. Also, if we receive a wait of 1.5 characters at any point, we must trigger an error message. Also, it appears as though this message is little endian. The logic is simplified as the following:

block-on-read:
    read until 3.5 delay
    check for errors
    decode

The following table is a listing of the baud wait times for the specified baud rates:

------------------------------------------------------------------
 Baud  1.5c (18 bits)   3.5c (38 bits)
------------------------------------------------------------------
 1200   13333.3 us       31666.7 us
 4800    3333.3 us        7916.7 us
 9600    1666.7 us        3958.3 us
19200     833.3 us        1979.2 us
38400     416.7 us         989.6 us
------------------------------------------------------------------
1 Byte = start + 8 bits + parity + stop = 11 bits
(1/Baud)(bits) = delay seconds
buildPacket(message)

Create a ready to send modbus packet.

Parameters:

message – The populated request/response to send

decode_data(data)

Decode data.

frameProcessIncomingPacket(_single, callback, slave, _tid=None, **kwargs)

Process new packet pattern.

method = 'rtu'
recvPacket(size)

Receive packet from the bus with specified len.

Parameters:

size – Number of bytes to read

Returns:

sendPacket(message)

Send packets on the bus with 3.5char delay between frames.

Parameters:

message – Message to be sent over the bus

Returns:

class pymodbus.transaction.ModbusSocketFramer(decoder, client=None)

Bases: ModbusFramer

Modbus Socket Frame controller.

Before each modbus TCP message is an MBAP header which is used as a message frame. It allows us to easily separate messages as follows:

[         MBAP Header         ] [ Function Code] [ Data ]         [ tid ][ pid ][ length ][ uid ]
  2b     2b     2b        1b           1b           Nb

while len(message) > 0:
    tid, pid, length`, uid = struct.unpack(">HHHB", message)
    request = message[0:7 + length - 1`]
    message = [7 + length - 1:]

* length = uid + function code + data
* The -1 is to account for the uid byte
buildPacket(message)

Create a ready to send modbus packet.

Parameters:

message – The populated request/response to send

decode_data(data)

Decode data.

frameProcessIncomingPacket(single, callback, slave, tid=None, **kwargs)

Process new packet pattern.

This takes in a new request packet, adds it to the current packet stream, and performs framing on it. That is, checks for complete messages, and once found, will process all that exist. This handles the case when we read N + 1 or 1 // N messages at a time instead of 1.

The processed and decoded messages are pushed to the callback function to process and send.

method = 'socket'
class pymodbus.transaction.ModbusTlsFramer(decoder, client=None)

Bases: ModbusFramer

Modbus TLS Frame controller.

No prefix MBAP header before decrypted PDU is used as a message frame for Modbus Security Application Protocol. It allows us to easily separate decrypted messages which is PDU as follows:

[ Function Code] [ Data ]

1b Nb

buildPacket(message)

Create a ready to send modbus packet.

Parameters:

message – The populated request/response to send

decode_data(data)

Decode data.

frameProcessIncomingPacket(_single, callback, _slave, _tid=None, **kwargs)

Process new packet pattern.

method = 'tls'
class pymodbus.transaction.ModbusTransactionManager(client, **kwargs)

Bases: object

Implement a transaction for a manager.

The transaction protocol can be represented by the following pseudo code:

count = 0
do
  result = send(message)
  if (timeout or result == bad)
     count++
  else break
while (count < 3)

This module helps to abstract this away from the framer and protocol.

Results are keyed based on the supplied transaction id.

addTransaction(request, tid=None)

Add a transaction to the handler.

This holds the request in case it needs to be resent. After being sent, the request is removed.

Parameters:
  • request – The request to hold on to

  • tid – The overloaded transaction id to use

delTransaction(tid)

Remove a transaction matching the referenced tid.

Parameters:

tid – The transaction to remove

execute(request)

Start the producer to send the next request to consumer.write(Frame(request)).

getNextTID()

Retrieve the next unique transaction identifier.

This handles incrementing the identifier after retrieval

Returns:

The next unique transaction identifier

getTransaction(tid)

Return a transaction matching the referenced tid.

If the transaction does not exist, None is returned

Parameters:

tid – The transaction to retrieve

reset()

Reset the transaction identifier.

Modbus Utilities.

A collection of utilities for packing data, unpacking data computing checksums, and decode checksums.

pymodbus.utilities.default(value)

Return the default value of object.

Parameters:

value – The value to get the default of

Returns:

The default value

pymodbus.utilities.pack_bitstring(bits: list[bool]) bytes

Create a bytestring out of a list of bits.

Parameters:

bits – A list of bits

example:

bits   = [False, True, False, True]
result = pack_bitstring(bits)
pymodbus.utilities.rtuFrameSize(data, byte_count_pos)

Calculate the size of the frame based on the byte count.

Parameters:
  • data – The buffer containing the frame.

  • byte_count_pos – The index of the byte count in the buffer.

Returns:

The size of the frame.

The structure of frames with a byte count field is always the same:

  • first, there are some header fields

  • then the byte count field

  • then as many data bytes as indicated by the byte count,

  • finally the CRC (two bytes).

To calculate the frame size, it is therefore sufficient to extract the contents of the byte count field, add the position of this field, and finally increment the sum by three (one byte for the byte count field, two for the CRC).

pymodbus.utilities.unpack_bitstring(data: bytes) list[bool]

Create bit list out of a bytestring.

Parameters:

data – The modbus data packet to decode

example:

bytes  = "bytes to decode"
result = unpack_bitstring(bytes)