[?]: Modbus RTU connection between PC and S7-200

[Lament]

Hi all,

I have an assignment which requires us to establish a modbus RTU connection between a PC and a S7-200(CPU 224) using PPI cable however CPU 224 failed to respond(there is no response at all).


I am using Lookout's program on PC(and i'm quite sure this program is correct ).

I am also using Modbus RTU instruction library for S7200.My ladder link is shown behind.I think it's correct too 'cause i take it from s7-200 manual.

http://www.esnips.com/nsdoc/c3afdc63-19 ... c4e351dfb3

My PPI cable switch is configured as following :

From left to right is :
1 2 3 4 5 6 7 8
0 1 0 0 0 0 0 0
(9600 baud, freeport mode ,local ,11 bit ).

Are these above things right ? (let's assume that my Lookout's program is correct ).
I get stuck at this point for a while so i need ur advises.

I'll appreciate all ur suggestions
Thank U in advance!

[rataman]

Are you using a serial or USB PPI adapter?
If you are using a serial one, use a REAL serial port, not an usb-to-serial.
Did you initialize Port 0 to FreePort,9600,etc etc ?
You should try using a single 232-485 converter and redirect Lookout to a serial port if that is possible. Look for Port 0 diagrams on S7-200 Manual.
I was not able to see your ladder program.

[Lament]

Are you using a serial or USB PPI adapter?
If you are using a serial one, use a REAL serial port, not an usb-to-serial.
Did you initialize Port 0 to FreePort,9600,etc etc ?
You should try using a single 232-485 converter and redirect Lookout to a serial port if that is possible. Look for Port 0 diagrams on S7-200 Manual.
I was not able to see your ladder program.

hi rataman,

I am using serial PPI cable and a real serial port .

I also tried to communicate through a 232-485 converter with A line connected to pin 8 at Port 0 and B line wired to pin 3 at port 0.

I also read the ladder program on S7-200 Manual including 2 networks : MBUS_INIT and MBUS_SLAVE(just copy and paste).

However, U remind me to initialize Port 0 to FreePort and i didn't do this before .Should it be necessary ? 'Cause in MBUS_INIT did have the mode=1 ( according to the manual , " an input value of 1 assigns port 0 to
Modbus protocol and enables the protocol" )

I'm not sure and I can initialize Port O to FreePort by setting up the SMB30,cann't I ?

[rataman]

Checking an old program it is not necessary to set anything on Port 0 , MBUS_INIT does it.
This is a single program i wrote just to put a 200 as a Profibus-Modbus converter:
SIMATIC 200 Station.mwp
http://www.sendspace.com/file/g9rrvg

However, have you tried with another program or just with Lookout?
Try this one:
Modbus_Poll_v3.60.rar
http://www.sendspace.com/file/zb3341
or
http://plcforum.uz.ua//Mo ... _v3.60.rar
I always test any modbus slave with it before connecting to a master, so you will be able to discard connection and PLC problem.


I hope this help.

[singleperson]

Dear All,

Do you have any expirenment about S7-200 Modbus RTU?
Please help me?

How to connect between S7-200 and Other device ( support Modbus)?

Thanks