S7 200 Modbus

Dear All
Can any one help me for modbus communication between
S7 200 CPU 224XP and PID temperature controller having serial port.My aim is only write temperature SP and read Act Temperature
What I have do
1. Connect temperature controller to PLC port 0

as
PLC PORT Pin Temp Controller
3---------------------------------> RS 485 (N)
8---------------------------------> RS 485 (P)

But now i am confused for

CPU 224 XP configure as Modbus master or slave mode?

Pls help me for the task
Also if anybody has sample project pls send

I have Modbus library installed with Microwin 4.0 SP5

Here is attache temperature controller manual

Waiting for help
Thanks

On the PID500 controller side,

Holding Tegisters will have the setpoint and the process variable. Holding registers are in the 4xxxx address range. The document doesn't show the leading 4, but it's 'understood'.

Holding register address 40021 appears to have the setpoint, mysteriously labeled 'zone setpoint 1', probably as a signed integer value, given its range of -1999 to 9999.

I'm perplexed about what they call the Process Variable (actual temperature). It's pretty obtuse to not have a Process Variable (PV) right up front in the map.

Maybe holding register 40003 is the PV because I'm speculating that in the absence of something clearly labeled "process variable" 40003 might be the PV, even though the term 'Resolution' appears for 40003. Resolution is probably intended for 40004 but the table is misprinted and where it says 'Resolution' it should say 'Process Variable'?

Or maybe holding register 40007 aka "Display value scaling point", ranged of -1999 to 9999 is the PV?

Likewise, these 'maybe' PV's are probably signed integers.

Sorry, I can't help you on the Siemens side, other than the Siemens must be a Modbus Master. Modbus slaves cannot talk to one another.

You might want to take a look at the exercise dahnuguy went through

http://www.plctalk.net/qanda/showthread.php?t=49659&page=2

trying to get his S7 to run as a Modbus master.

Pay particular attention to his post #24 (the last one, make sure the page advances to post #24).

Dear Sir
Siemens S7 200 can work as modbus master
Pls see attached screenshots of microwin software
Pls help me to configure it as a master and communicate with teperature controller

Pls see attached sreen shots
S7 200 can works as modbus master
Pls help for the configuration of S7 200 as modbus master

Problem is solved
simply reverse the wire of P & N at temperature controller end
It works fine
Thanks

Is address 40003 the process variable?

Dear Sir
The process veriable adress is 40183,40184,40185
Thanks