Asynchronous Asyncio Serial Client ExampleΒΆ

from pymodbus.compat import IS_PYTHON3, PYTHON_VERSION
if IS_PYTHON3 and PYTHON_VERSION >= (3, 4):
    import asyncio
    from serial_asyncio import create_serial_connection
    from pymodbus.client.async.asyncio import ModbusClientProtocol
    from pymodbus.transaction import ModbusAsciiFramer, ModbusRtuFramer
    from pymodbus.factory import ClientDecoder
else:
    import sys
    sys.stderr("This example needs to be run only on python 3.4 and above")
    sys.exit(1)


# ----------------------------------------------------------------------- #
# configure the client logging
# ----------------------------------------------------------------------- #
import logging
logging.basicConfig()
log = logging.getLogger()
log.setLevel(logging.DEBUG)

UNIT = 0x01


async def start_async_test(client):
    # ----------------------------------------------------------------------- #
    # specify slave to query
    # ----------------------------------------------------------------------- #
    # The slave to query is specified in an optional parameter for each
    # individual request. This can be done by specifying the `unit` parameter
    # which defaults to `0x00`
    # ----------------------------------------------------------------------- #
    log.debug("Reading Coils")
    rr = client.read_coils(1, 1, unit=UNIT)

    # ----------------------------------------------------------------------- #
    # example requests
    # ----------------------------------------------------------------------- #
    # simply call the methods that you would like to use. An example session
    # is displayed below along with some assert checks. Note that some modbus
    # implementations differentiate holding/input discrete/coils and as such
    # you will not be able to write to these, therefore the starting values
    # are not known to these tests. Furthermore, some use the same memory
    # blocks for the two sets, so a change to one is a change to the other.
    # Keep both of these cases in mind when testing as the following will
    # _only_ pass with the supplied async modbus server (script supplied).
    # ----------------------------------------------------------------------- #
    log.debug("Write to a Coil and read back")
    rq = await client.write_coil(0, True, unit=UNIT)
    rr = await client.read_coils(0, 1, unit=UNIT)
    assert(rq.function_code < 0x80)     # test that we are not an error
    assert(rr.bits[0] == True)          # test the expected value

    log.debug("Write to multiple coils and read back- test 1")
    rq = await client.write_coils(1, [True]*8, unit=UNIT)
    assert(rq.function_code < 0x80)     # test that we are not an error
    rr = await client.read_coils(1, 21, unit=UNIT)
    assert(rr.function_code < 0x80)     # test that we are not an error
    resp = [True]*21

    # 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).

    resp.extend([False]*3)
    assert(rr.bits == resp)         # test the expected value

    log.debug("Write to multiple coils and read back - test 2")
    rq = await client.write_coils(1, [False]*8, unit=UNIT)
    rr = await client.read_coils(1, 8, unit=UNIT)
    assert(rq.function_code < 0x80)     # test that we are not an error
    assert(rr.bits == [False]*8)         # test the expected value


    log.debug("Read discrete inputs")
    rr = await client.read_discrete_inputs(0, 8, unit=UNIT)
    assert(rq.function_code < 0x80)     # test that we are not an error

    log.debug("Write to a holding register and read back")
    rq = await client.write_register(1, 10, unit=UNIT)
    rr = await client.read_holding_registers(1, 1, unit=UNIT)
    assert(rq.function_code < 0x80)     # test that we are not an error
    assert(rr.registers[0] == 10)       # test the expected value

    log.debug("Write to multiple holding registers and read back")
    rq = await client.write_registers(1, [10]*8, unit=UNIT)
    rr = await client.read_holding_registers(1, 8, unit=UNIT)
    assert(rq.function_code < 0x80)     # test that we are not an error
    assert(rr.registers == [10]*8)      # test the expected value

    log.debug("Read input registers")
    rr = await client.read_input_registers(1, 8, unit=UNIT)
    assert(rq.function_code < 0x80)     # test that we are not an error

    arguments = {
        'read_address':    1,
        'read_count':      8,
        'write_address':   1,
        'write_registers': [20]*8,
    }
    log.debug("Read write registeres simulataneously")
    rq = await client.readwrite_registers(unit=UNIT, **arguments)
    rr = await client.read_holding_registers(1, 8, unit=UNIT)
    assert(rq.function_code < 0x80)     # test that we are not an error
    assert(rq.registers == [20]*8)      # test the expected value
    assert(rr.registers == [20]*8)      # test the expected value


# create_serial_connection doesn't allow to pass arguments
# to protocol so that this is kind of workaround
def make_protocol():
    return ModbusClientProtocol(framer=ModbusRtuFramer(ClientDecoder()))


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    coro = create_serial_connection(loop, make_protocol, '/dev/ptyp0',
                                    baudrate=9600)
    transport, protocol = loop.run_until_complete(asyncio.gather(coro))[0]
    loop.run_until_complete(start_async_test(protocol))
    loop.close()