Could anyone suggest me a solution to this problem it would be very helpful for me.
I also tried to employ some timing mechanism to fire the messages ( like the messages are fired sequentially one after other based on a timer) but this also doesn't seem to work, in this scenario all the messages error and no message gets done. I hope this errors can be controlled or minimized if I am able to set the polling interval of the Modbus messages(the same as we do in prosoft modbus modules), but micrologix 1100 modbus message setup does not seem to have such setting ( it only has slave timeout option, which is not of much use in this case). This is too small as regards to modbus polling. As I watched the Scan time of the PLC it is about 2 miliseconds. Ie:- it errors for 3-4 times and then again gets done and the cycle continues.( I am incrementing two counters for each message to count how many times its DN and ER bits fire to judge the message successful completion rate) This results that the data I am receiving is not received in proper timing and is generally slow updating due to those errors. The problem I am facing is that each message errors intermittently and gets done once only after is errors for say about 3-4 times, this is happening with each and every message. As far as Modbus polling is considered I am having no problem in polling the feeder relays, in read as well as write operations and I am able to do them, but not in a satisfactory way. This means I am sending in total 8 Read and 8 Write messages (Total 16) to communicate with those Feeder Protection relays.
#Read error modbus poll code
There are about 8 feeder protection relays from which I am reading 20 integers each by sending messages on channel 0 and the function code is "Read Holding Registers" also I am sending a "Write multiple coils" message for each relay to start and stop it over modbus. I have a Micrologix 1100 PLC which I have configured as a MODBUS RTU Master to communicate with Modbus Compatible feeder protection relays daisy chained using an appropriate cable and 1763-NC01 cable.
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