Siemens HMI and MPI

Do I need to puchase an MPI adapter when using a Siemens HMI?

No. It depends on the model though, of course.

For example, the MP370 series have MPI,RS-232,RS-422/485 and Ethernet options to communicate.....

I'm sorry to crowd your conversation ,but I need to get more involved in the troubleshooting of another plant. Could you explain what the MPI adapter is for, and how does it work.

Thanks in advance,

MPI/DP is a Siemens protocol that supports up to ** devices, similar to that of Controlnet,DeviceNet, etc.
(Typical node system)

I am sure that the more experienced Siemens people can elaborate on this...

The simple answer is, no.
A 300/400 series plc has a 9 pin programming port built in which you can connect to the multipanel. ("2DP" versions have an additional profibus port). To reliably connect (Up to 50m) on MPI = multi point interface, use D-connectors with built in terminating resistors. Switch these on at both ends of the network. Use a "Programming" plug at the plc, which has a socket on the back so you do not have to unplug your hmi to edit/monitor the plc.

The multipanel can be programmed via an rs232 cable but the plc will need a Siemens adaptor (and software!!!).

Hope this helps