Pymodbus – Listen for input change on PLC device

I am programming a PLC device (Moxa ioLogik E1214) and have connected the DI ports to buttons, and the coils are connected to LED lights. The idea is that when you press a button, the LED should light up.

I have gotten the program to work if you hold down the button until the read input function executes. The problem is that I'd like to set a time frame (X seconds) and if the button is pressed (and not held down) within this timeframe the light should toggle.

The code is below:

import time
import logging
logging.basicConfig()
log = logging.getLogger()
log.setLevel(logging.DEBUG)

from pprint import pprint
from pymodbus.client.sync import ModbusTcpClient as ModbusClient

moxaA = ModbusClient('XX.XX.XX.XX', port=502)

print "Press a button now"

time.sleep(2)
result = moxaA.read_input_registers(0x30, 1)
if result:
    pressedBtn = result.registers[0]
    if pressedBtn == 1:
        moxaA.write_coil(0, 1)
    else: 
        moxaA.write_coil(0, 0)

As you can see I've set a timeout for the reading of the input registers. But how can I "listen" for an input change within these seconds, and not have to hold the button down until the read input registers function executes?

Thanks in advance

Solution

You forgot some arguments (unit, connect, isError()).

I improved your snippet code:

moxaA = ModbusClient('XX.XX.XX.XX', port=502)

if moxaA.connect()
    print "Press a button now"
    time.sleep(2)
    result = moxaA.read_input_registers(0x30, 1, unit=1)

    if not result.isError():
        pressedBtn = result.registers[0]

        if pressedBtn == 1:
            moxaA.write_coil(0, 1, unit=1)
        else: 
            moxaA.write_coil(0, 0, unit=1)

[NOTE]:

With the above sleep(2) you should press the button 2 seconds or after 2 seconds.
isError() defined in the pymodbus 1.4.0 and above.
You should specify the unit, in many cases unit is equal 1.