Posted 21 Nov 2019 (edited) hello I have been forced to replace a TWDLMDA20DRT with a Schneider TM221ME16R. the plc is a slave but I am having trouble getting the Modbus data exchange to work like it did with the old plc. I have setup the serial port to use Modbus etc etc and I played about with the read_var FB but this wasn't required in the old plc so im confused as to why I would need to use it on the replacement. I have come across another FB send receive message but again i'm not too sure if this is required. the master plc uses the msg2 and exch2 command. I believe I am just missing something very simple here. Lighting Panel - Old_PLC.twd Lighting Panel1 - Master -.twd Lighting Panel - Pillar5 -.smbp Edited 21 Nov 2019 by danmckillop Share this post Link to post Share on other sites