Sycon multi drop protocol (SMDP)

[BenJones 1]

Hello, A company (Cryomech) supply us with a cryocooler and this has a controller made by a company (Sycon). I wish to connect to the controller to my PLC (Fx3u) using a serial card (RS485_ADP). I'm also using IEC developer. The protocol in question (SMDP) is not well known and they haven't got around to re-programming it with an industrial standard protocol like modbus or profibus. This of course makes things more tricky to program and I can assure you that I'm NOT the best programmer in the world ! The Mitsubishi guy say I'll have to program my own driver using the RS2 non-protocol. I have got no idea how to do this. I've got RS2 function block to work before (with Beijers modbus solution pack) using Modbus RTU but the SMDP uses ASCII. I don't know to program ASCII or even know if this is possible with the Mitsubishi stuff. Any pointers in the right direction would be useful. I've attached the protocol reference manual. Thanks, Ben data_dictionary.pdf Sycon Multi Drop Protocol II.pdf

[JRoss 84]

It's not too bad. The FX3U has a lot of built in commands for converting to/from ASCII (aka Strings). Essentially what you'll be doing is assembling and parsing strings of ASCII characters based on the formats described in the protocol manual. The RS2 command just sends and receives the strings from the Sycon controller. The real work is for you to figure out what the strings you need to send/receive will look like. Most likely you will not need all the commands and data available, so you won't need to write a full protocol. Just decide what you need, figure out what the strings will look like, then write the logic to assemble the commands and parse the responses. It might be helpful to use a telnet client on your laptop to test the RS2 command and make sure the ASCII send/receive is working properly. Then when you think you have it, hook up to the Sycon! Let us know if you have any other questions. Good luck.