OMRON Modbus Rtu Slave

Quick introduction:
Hi, I'm 22, I recently got my degree and I only have 5 month experience on Industrial Automation and just the very basic knowledge about OMRON/CX-Programmer. (Also my english isn't that well and this is my first thread in this forum).


My doubts:
At this moment I was asked to change one CJ2M's program (in Ladder, and the PLC is the slave) in order to make a list of desired variables "readable" by the master (an host computer/ SCADA) wich is using the protocol MODBUS-RTU. I only have to work on the PLC' side and i only know the name of the variables (all digital inputs) and their corresponding address.
I already read the "CS/CJ Serial Communication Unit Operation Manual" but i still have some doubts:


- The only way to define my slave address is done by writing a code to put the value of the address on the corresponding bits of DM area? or can i define the address using some feature of CX-Programmer?


- (A CJ1W-SCU41-V1 is already implemented in the field) on the slave'side i only have to make sure the variables are allocated on the right place, according to the master's commands and modbus' addresses, right?


- I read something related to the frames sended by the slave as responses for each master's command, am I supposed to write some code to this task or it is done automatically?


- Imagine the master is using the "Read coils" command, in OMRON there are 4 memory area associated to this data model "Coil" by default it is associated to CIO area, can i switch in the slave to Holding area without problem?




Sorry about my english and this extensive text. Thanks.

Should i be more specific? Is my english that bad? Is my question out of topic?

I have no way to test it before i go to the cliente's instalation since all the hardware is already there, that's why i need to take this doubts. I already search alot in this kind of forums but the majority only describes the MODBUS-RTU when PlC is the master wich is not my case.

Patience butterfly - many of us are really busy making a $ or two - which port is the SCADA to read from? RS232 or 485? I gather you want a Modbus RTU slave? Which processor? At the very least you will have to go into the I/O table and double click on the SCU41-V1 card to set it up. Snips attached for minimum setup - you can select speed, bits and slave number. You can also select where you want the data to be - CIO, DM and the like. If you select DM for example then you can put info where you want. If you place info starting in DM1000 then the direct address for the SCADA would be holding register 1000 - if DM0000 holding register 0. The snips are port 1 - same setup if port 2.

Thanks for your reply Sir, I did not want to be rude or look impantient, it was my first thread so i was not sure if something was wrong, by the way:



Yes i want MODBUS-RTU slave, and i'm using the RS232 port wich is PORT 2 according to the manual.


The CPU unit is the CJ2M-CPU33.


Thanks for clarifying that i can select on the slave's side where the data is going to be read by the master, but these areas also depend on the commands sent by the master, so i should know wich is being used by the master and follow the manual's table wich contains that information, rigth?


Another thing the manual doesn't especify is if i must code the program in order to make the slave send back those "response frames" described for each command.

No - when you select the port as Modbus Slave it will do all the responses for you. If you leave the settings for memory area as default holding registers will be DMs. Then you just move the data you want them to receive to the DMs. I do not use bits at all but consolidate the bits into words - they can then break them out as they wish. Just send them a list of holding registers and list which bits are what.