running 19.2Kps MPI port using RS485

[dsc 1]

As we know s7-300 MPI is actually RS485 with much higher baud rate, in this case if we drop its baud rate down to 19.2K, then we can monitor its communication signal using Rs485 to RS232 converter, right? Now i have simple IPC application which need to read/write some value from s7-300 PLC, my IPC already have RS485 port build in. I am thinking is that possible i just use that RS485 port to communicate with MPI (using 19.2K baud rate) without using any adapter? (i can use USB/MPI adepter to set the baudrate drop to 19.2K first) Anyone have experiences on this? any ready-made windows driver for that? Thankyou.

[Mike Dyble 0]

Have a look at http://libnodave.sourceforge.net/index.php, but I am not sure that it will be easy, as libaries use the MPI adapter, It worth remembering that the MPI adapter does more than change the baud rate, it also does some of the token handling. Will probably be easier to use an MPI adapter.

[dsc 1]

MPI adapter is not cheap, if i could use buildin RS485 port, i would prefer to do so. I used to monitor profibus signal (with 19.2K baud rate) using RS485 to RS232 converter also, i know it is possible, we just have to know the protocal or have the right driver for it.

[Mike Dyble 0]

MPI protocol is not 'published', however someone may have reverse engineered it, but if they have I have never come across it. Would Profibus be the answer, does the port support Profibus, if so there is quite a bit published on profibus, that may be a way forward.

[JesperMP 2]

No. It is between the PC and the MPI adapter that you have 19.2 kbs (in some cases). MPI can be dropped to 19.2 kbps, but that would not help, because there is no puplic information about the MPI protocol. You still need a PC adapter to make the connection between a PC and MPI.Libnodave requires a PC Adapter, or ethernet via a CP, or Simatic Net. Ethernet may be the better way to go for you. With S7-300 it will be expensive because you have to add a CP343-1 or use at least a 315-2PN/DP. The new IM151-8 CPU for ET200S may be intereting for you. It has ethernet only (no MPI), and costs approximately the same as a 314. You would then have to get a library that talks ethernet. There is Simatic IE Softnet Lean. 400 Euro per installation. And there is Deltalogic Accon-AGLink S7-TCP/IP. 3000 Euro per developer.

[dsc 1]

The software package you suggest is alot more expensive than the MPI adepter itself, i would rather use Libnodave which is free and able to do the same things via ethernet. Anyway I already found the MPI protocal in some china industrial forum and will try that out soon.

[JesperMP 2]

Libnodave requires a CP343-1. It wont work with the onboard PN port on a 315-2PN/DP or an IM151-8 PN for example.If this was my task, I would go ethernet and either just get Softnet IE Lean (if it is 1-2 projects only), or the Deltalogic library (if this is for everal projects). Siemens is going more and more Ethernet, which is logical. MPI has had its day.