Read ASCII string to S7-300

I've connected a system as below:

(PM4 Ins, add1)------>>returned ASCII String>>----RS485port(S7-300)
(PM4 Ins, add2)---|
(PM4 Ins, add3)---|
(PM4 Ins, add4)---|
(PM4 Ins, add5)---|


Anyone who can help me how to read this ASCII string(How the PLC can be programed to read this string)from each PM4 Ins, using "Poll"?

Thanks a lot!!!

Hello ALU;

If you are using a 31x-PtP CPU, there is a Getting Started document for (amongst other things) ASCII communication that could help you:

http://support.automation.siemens.com/WW/view/en/15390497

If your CPU has only a standard MPI or Profibus-DP port, you cannot use it to communicate with ASCII devices, you would need a CP340 or CP341 serial comm. processor in your rack.

please specify the hardware you have on hand, we may be able to help you more.

Hope this helps,

Daniel Chartier

Hi Daniel Chartier
Thank you for your reply.

I give more detail of my system as below:

(Display,#1)------->>returned ASCII String>>----RS485port(CPU31x-2PtP; CPU31x-2DP+CP340)
(Display,#2)---|
(Display,#3)---|(Rs485)
(Display,#4)---|
(Display,#5)---|

The Display is connected to 14Bit Absolute Encoder to display rotation degree (running), and it has RS485 port returned the value on display in ASCII, I have 05 Displays which are assigned the address from #1 to #5, now i am wondering to used CPU31x-2PtP or CPU31x-DP with CP340 as your sugestion, the PLC also connect to SCADA...
Please give me some more sugestion...
Your suggestion is helpfull to me..
Thank you.

By the way, I want to know how to expand I/O with CPU 31x-2PtP?