BBPrudente

Hello,

I'm developing an application with 2 S7-1200, 3 ET-200S and 11 G120C inverters. With profinet i got everybody online... util... I get a not Siemens device that only works with Modbus RTU... Than I got a CM 1241 and got online with it. BUT, I cant comunicate more than 32 Words, is it an limitation of Modbus RTU? Or from the CM1241? Or I'm missing something?

In attach my configs.

ps.: I already used a pointer in the MB_HOLD_REG parameter, i used ( P#DB11.DBX0.0 BYTE 128 ) for a 128 bytes length, and it didnt workd to)

THANKS

smiffy

The limits for modbus RTU are:-
Read 125 words (registers)
Write 123 words (registers)
Read 2000 digitals (bits)
Write 1968 digitals (bits)

So why you cannot read more than 32 words is not an issue with the modbus protocol.
I would suggest that you have a coding error somwhere in your code.
As has already been asked what error codes are being shown on the block or returned to the master (exception responses)?

smiffy

But in that case, the slave device would, I expect, return and exception response (with error code 02 or 03). If that were the issue wouldn't the S7 master indicate that it had received said exception response? (via the STATUS code I assume).

The ERROR bit is TRUE for one scan, after the last request was terminated with an error. The error code value at the STATUS parameter is valid only during the single scan where ERROR = TRUE. ( Easily missed by user if not stored )

Cheers

Navnag