Omron Modbus TCP Read - Shift Results

[bernie_carlton]

(Note: also posted at MrPLC)

The results from a Function 03 (Read) splits the high/low byte of the returnd 16 bit words. Neither of the 4 bit shifts (SLD./SRD) seem to shift the correct direction across multiple words. Has anyone dealt with this? (CP1H with CP1W-MODTCP01-US adapter)

 

[LadderLogic]

(Note: also posted at MrPLC)

The results from a Function 03 (Read) splits the high/low byte of the returnd 16 bit words. Neither of the 4 bit shifts (SLD./SRD) seem to shift the correct direction across multiple words. Has anyone dealt with this? (CP1H with CP1W-MODTCP01-US adapter)

Could you just multiply/divide by 16?

 

[bernie_carlton]

It's a tabel of 16 bit registers shifted by 8 bits across word boundaries. (High byte of one word shifted to the lower byte of the next lower addressed word. This is in the Modbus received buffer and is a normal artifact of Modbus. But other PLC's do the re-alignment for you. Not this one.) Neither of the provided multi-bit shifts work correctly across the word boundaries. If necessary I'll have to do a whole mess of masking and shifting. I'm hoping for a more elegant solution.

 

[lostcontrol]

The Modbus Easy Master @ MrPLC has examples of doing this. With the Serial version, shifting bytes across & up/down is required to generate the send requests, as well as having to decipher the received message.

Creating a loop to do this is easy enough, I have done it in both ladder & ST in the past..

 

[bernie_carlton]

Thanks, I finally found the example.

'Easy Modbus' my a$$!

 

[LadderLogic]

'Easy Modbus' my a$$!

Well, of course it is not easy when it is not supported by the PLC and has to be done via byte-pushing, like in this case.

Otherwise it is OK.

 

[bernie_carlton]

I wasn't saying 'Modbus' is the problem, it's the implementation in the PLC as you mentioned. In the AB Micrologix line and in AutomationDirect is done for you. My mind is now officially fried from staring at indexed moves. Back at it tomorrow.