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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
Contributors
- Patrick McDonagh - @patrickjmcd - Owner
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