Newbie needs RS232 communication info

[stickben]

Hello, I am new to PLCs (but not embedded development) and I need some things cleared up about the project that I am working on. The device that I am working with is a FX1N with the 232-BD attachment. I am trying a little reverse engineering to better understand the software that I am trying to fix. The PC application periodically sends a string of data to the FX1N, I am assuming that the data gets written directly to the FX1N's memory somehow because the ladder code does not make any mention of the RS232. Anyway, I read the spec for Mitsubishi about communications, but the data that I am seeing sent out does not seem to match up with the spec. Can someone help me decode what I am seeing? There are 2 functions that get called all the time, write and read. the write data function sends out a 0x02 (this part matches to the start of text character) and then sends out this, E1040E61000000000000000000000000000000100 followed by a 0x03 ( end of text) The read function does something similar. Where is this data being stored to on the FX1n? Thanks, Ben

[waynes]

hi stickben, i am assuming that the author used RS instructions. therefore, you must look for the RS instruction somewhere in the code. The RS works like this RS d200 k11 d500 k50 where: d200 is the data you send d500 is the data you receive k11 is the amount of data you send k50 is the amount of data you receive Hope this helps

[stickben]

Well, through some painfull reverse engineering, I found that the OS on the PLC is actually writing data from the rs232 board directly into RAM. So it looked like data was somehow mysterously appearing on the PLC side. Mystery solved. Thanks, Ben