Hello all,

I have some questions regarding modbus TCP/IP communication of S71200 with energy meter PAC 3200, that may be discussed before. 

1. I see that there are some registers in PAC that has address beyond 50000. in help of MB_CLIENT block, I see that permissible range for MB_DATA_ADDR parameter is upto 49999. So how can I access registers beyond 50000?

2. I want to communicate with multiple servers. If my cpu supports maximum 8 connection resources in open user communication, then I can only communicate with 8 different IP address or I can make IP address dynamic from PLC program and communicate with 255 devices?

Hope my questions are clear.

Kbv.

Maybe that this can help you....

Data Communication between S7-1200 and SENTRON PAC3200 via MODBUS TCP (Set 22)

Hi. 

I have made a modbus library, that has a ready block for the PAC3200. Unfortunately the library doesn't support disconnecting, so it would not be possible to connect to 8 devices. I think a S7-1200, only support 5 TCP-connections. 

If the PAC devices are close to the PLC, then an other way to get around the connection limit, is to insted use modbus-rtu. The mb_master block use significant less memory then mb_client, and memory is limited on a S7-1200. 

With the library it's quite easy to extend the the number of PAC3200 devices.

The library itself can be found at the following link:
https://github.com/olab84/rexhip

Hello all,

thanks for clarifications.

So just to be clear, if my PLC has 8 connection resources I can use only 8 call of MB_client at a time and even if I use 8 different blocks for 8 different servers, I can connect to only 1 at the time, means disconnect bit must be 1 for all but 1 MB_client block.

But I can use only one block and change its parameters from my user program. I will write polling logic for changing IP addresses every second or so, then this way I should be able to communicate to many devices. Of course, more devices means more update time, but if that is not the constraint then I think it should work fine. Any advice?

Kbv.