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Pycomm Scanlist

Python module for managing a list of tags being read from a Rockwell Automation PLC.

Scanlist Class

The module implements a Scanlist class with a required parameter of IP Address. Optionally, a plc_type and a change_handler parameter can be passed to the class.

plc_type parameter

Due to different implementations within pycomm for Micro800 PLCs, in order to read from a Micro800 PLC, the value of plc_type must be "Micro800". The default value for plc_type is "CLX" for ControlLogix/CompactLogix PLCs.

change_handler parameter

The change_handler should be a function with a required parameter sender and an optional parameter eargs. sender is a reference to the instance of Tag that has changed.

The default implementation of change_handler is:

def change_handler(sender):
    """Handle a tag value change."""
    print("{} changed from {} to {}".format(sender.tag_name, sender.last_value, sender.value))

Scanlist.add(tag_name) function

Scanlist.add takes one parameter tag_name and adds it to the list of tags to scan.

Scanlist.remove(tag_name) function

Scanlist.add takes one parameter tag_name and removes it from the list of tags to scan.

Scanlist.print_tag_names() function

Scanlist.print_tag_names() prints all tag names currently in the list of tags to scan.

Scanlist.scan() function

Scanlist.scan() polls all tags in the list of tags to scan and runs the change_handler function if the tag value has changed.

Example

The following example creates two scanlists, one for the Micro800 PLC at 192.168.1.12 and another for the CLX PLC at 192.168.1.11. Each PLC has 4 tags in the scanlist.

import time
from pycomm_scanlist import Scanlist

def handle_tag_change(sender, eargs=None):
    """Handle a tag value change."""
    print("{} CHANGED FROM {} TO {}".format(sender.tag_name, sender.last_value, sender.value))

micro_scan_list = Scanlist("192.168.1.12", plc_type="Micro800", change_handler=handle_tag_change)
micro_scan_list.add("pond1Volume")
micro_scan_list.add("pond2Volume")
micro_scan_list.add("pond3Volume")
micro_scan_list.add("pond4Volume")

clx_scan_list = Scanlist("192.168.1.11", change_handler=handle_tag_change)
clx_scan_list.add("DH_Fluid_Level")
clx_scan_list.add("DH_IntakePressure")
clx_scan_list.add("DH_IntakeTemperature")
clx_scan_list.add("DH_MaxIntakePressure_Forever")

micro_scan_list.print_tag_names()
clx_scan_list.print_tag_names()

while True:
    micro_scan_list.scan()
    clx_scan_list.scan()
    time.sleep(5)

TODO

  • Add tests to increase coverage.
  • Per-tag handlers?
  • PyPi package

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0.1

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