Siemens MPI, a 'new' manifestaion?!


Thread Starter

Roger Irwin

Siemens have brought out a new low cost touch screen which they tout as 'Specially designed to work with the S7-200'. You might think that it is a more elegant replacement for the veritable TD200. You may expect that it uses PPI (the native protocoll of the S7-200's). You would be wrong.

To use the TP070 you program it using the PC-PPI cable directly to the device (the 5611 is no good here!). You program the PLC using the standard
PPI port at 9600 or 19200 (don't ask me why you cannot use this port as 34000!). Then you connect the panel to the PLC and it works. If you also
connect the PC using PC/PPI cable (as you would do with a TD200), things stop working. In fact as soon as you put any other PPI master on the bus
only one master works at a time (so you cannot e.g. communicate between PLC's). Not slow to change the tocken (as is normal on a multi master PPI), but I mean locked up.

After making sure I had the masters on the lowest sequestial adreess, and playing around with the Gap facter, I decided to consult the manual, which
refers to the interface as 'MPI'.

Time to book a call to the Siemens helpline. I explain the setup and I am told that you cannot do it. A TP070 must be connected directly to a 200 PLC with no other device on the bus. MPI, I am told, stands for 'Monomaster
Point Interface'.

The difficulty with which Siemens connect to the rest of the world is legenendry. The degree of incompatibility between thier own products is

D. C. Pittendrigh

Hi All

There are 2 lessons here,

1) Siemens does not produce cheap solutions, elegant or otherwise.
2) Use Profibus DP only unless you can use Ethernet.

Good Luck
Donald Pittendrigh