Siemens Modbus addressing

Hi all,
Again another Modbus question, I have a s7 414-2 with a cp441 card I am sending and receiving data to deltav. Send block to deltav is db100 starting at Modbus address 40001(both AO & DO) receive block from deltav is db101 (bothAO & DO) starting at Modbus address 40513,
The problem is that I cant seem to receive any data on the Modbus address from deltav after 40553, up until this point all comms are fine, is this a config problem as if I am correct both systems should be able to address more than this!
Any help anyone!
Thx

maico said:

if I am correct both systems should be able to address more than this!

Click to expand...

I have experience with neither but experience with Modbus.

I find that the Modbus Standard provides a maximum limit on register transfer (125), but that implementations vary all over the place.

Some devices will not take more than a single register write, for example.

One device provided only 23 registers, attempts to get more than 23 failed. It wasn't documented, that's just the way it was.

So I have to ask, why do you think you are correct that the slave/server (DeltaV) should provide more than the 50 registers it is currently providing?

go with multiple read cycle with different data lengths say 32 word...
You will get the data...

I used a tool called CAS modbus scanner. Any modbus poller with an auto discover option will do. Launch it and it will simply map the data

When troubleshooting modbus problems you need a PC with modbus software that can act as a slave and as a master. There are a number of free ones on the net.

And of course a serial post with what ever interface you use RS232/422/485.

You want to communicate with delta v <-> PC and well as S7<->PC.
Then you can see what the problem is and what is sent.

You can also connect the PC so that you can read the traffic between S7 and delta V. This works best if you are using RS485 interface though as you only need one port on the PC to read both requests and replies.