Q Modbus Z.MBRQ instruction for IEC developer

[KenE 0]

Hello, I'm using GX IEC Developer 6.0 with a Q series ModbusTCP card (QJ71MT91). GX IEC Developer doesn't seem to have the Z.MBRW instruction available. It seems I can write Melsec IL with this instruction, but has anyone got a better way?

[tragically1969 0]

The Mitsubishi implementation of Modbus is a little awkward to configure and use on their cards but I ended up using the intelligent function utlity to configure reads and writes to the modbus slaves, what are you reading\writing from ?

[KenE 0]

I am needing to read one register from two different Cognex cameras. I need the update to be as fast as possible, so waiting for a periodic update might be a problem unless it could update every scan (< 1ms) or something like that. I thought I saw reference in the manual to how to have soem register areas updated in the "end processing" of the PLC, but I didn't see further reference to it (I'm in the process of reading up on it further). Any ideas? Thanks.

[tragically1969 0]

The easiest way is to to use the intelligent function utility, you can set all the things you have mentioned then leave the PLC to do its stuff. Essentially you use the IF utlity to setup which slave you are reading from, what you are reding, where to put what you are reading and how often, its a little tricky to setup but once done its a breeze, its all fairly well documented in the manual from page 8.8 onwards: http://194.130.244.64/branch/database/serv...loc&id=1694

[KenE 0]

The fastest auto update using GX-Config is 10ms, which is too slow for this application. What I ended up doing was using a Melsec IL pou with a bollean LD instruction trigger and the Z.MBRW instruction following it. I will do all of the other high level stuff in another POU or FB and trigger the read with the bit. It seems hokey, but hopefully future versions of IEC will have this instruction in the library.