Simple PLC program for testing Transnet radios.

Join Date
Jan 2018
Location
Alaska
Posts
1
I have two AB MicroLogix 1500s that I want to be able to communicate with each other via two Transnet 900 radios (one master, one remote). Using GE's software I have configured the radios so that they are connected, but I don't know how to tell the PLCs to send information back and forth.

Does anyone have a simple program I can use as a starting point? All I want is something I can use for testing. Send a random value from PLC A to B, and send a random value from B to A.

Forgive my noobiness - I have spent very little time actually programming PLCs.
 
Do you have the Micrologix 1500 with one or two serial ports?

You will likely want to set the serial port in both Micrologix used by the radio to DF1 Radio protocol or Modbus. I think if it is set for DF1 Radio protocol, you can still use RSLogix 500 to connect, but I am not 100% sure of that. If you set it for Modbus, you can't use it with RSLogix 500, so be prepared to use the DCOMM button to switch the port settings to normal DF1 Full Duplex.

You might be able to use the standard DF1 Full Duplex protocol for a simple point to point application, but that is something I have not tried either.

Your radios will have a baud rate that you need to match. I am not familiar with that model. Generally, for 900Mhz serial radios, the baud is limited to 9600, and with UHF it is limited to 4800. The radios and the Micrologix all need the same baud rate.

I would recommend setting up a read and a write in the "polling master" PLC. Often, with spotty radio links, the writes will succeed and the reads will fail.

Use the DN or ER bit from the first message to advance to the next. I normally put a time delay between each message. Radios almost always benefit from a little dead air time between messages. Sometimes 50ms is enough, other times a full second makes things work better depending on the type of device you are polling.
 

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