Siemens S7-1200 (CB1241 RS485) controlling Eaton inverter on Modbus RTU

Hi all,

I've hit a bit of a brick wall and need some help. I'm currently trying to get a Siemens S7-1200 PLC to talk to an Eaton DE1 Drive I'm using the CB 1241 RS485 Communication module, Wired like so:

M: Pin 1 (0V)
TA: Linked to T/RA
T/RA: Pin 7
T/RB: Pin 8
TB: Linked to T/RB
RTS:N/C

All I need is simple start and stop control with a speed reference, reading a fault from the drive would be handy if possible, also. This should be simple, but I just can't figure it out, I've only ever dealt with ethernet and profinet.

I've successfully loaded the MB_COM_LOAD FB and called it in the 'OB1' using the first scan bit. this loads without errors, I just can't figure out the MB_MASTER FB, what parameters need entering in it etc...

Hope you guys can help!

The DE1 Modbus RTU Manual:
ftp://ftp.moeller.net/DOCUMENTATION/AWB_MANUALS/MN040018_EN.pdf

TIA,
Sam

http://www.plctalk.net/qanda/showthread.php?t=100285

http://www.plctalk.net/qanda/showthread.php?t=109409

The above threads may help you out.
Regards,

Probably a typo but pin 1 on the drive is not 0V, it is pin 3, and that should be going to pin 5 on the CB1241.

BryanG said:

Probably a typo but pin 1 on the drive is not 0V, it is pin 3, and that should be going to pin 5 on the CB1241.

Click to expand...

Well spotted, yes it was indeed a typo!

gclshortt said:

http://www.plctalk.net/qanda/showthread.php?t=100285

http://www.plctalk.net/qanda/showthread.php?t=109409

The above threads may help you out.
Regards,

Click to expand...

Thanks for those examples. What I'm wondering is why there is '40001' or '40002' etc.. being sent to the drive?

aandjsam said:

Thanks for those examples. What I'm wondering is why there is '40001' or '40002' etc.. being sent to the drive?

Click to expand...

Modbus standards.
A 4 or a 3 and such will point to different locations such as "holding registers" "read single coil", "write single coil" and such.
Check out your Modbus mapping in the documentation for your device.
You should be able to find a description and the actual mapping in there.

bkottaras said:

Modbus standards.
A 4 or a 3 and such will point to different locations such as "holding registers" "read single coil", "write single coil" and such.
Check out your Modbus mapping in the documentation for your device.
You should be able to find a description and the actual mapping in there.

Click to expand...

That's fantastic, finally got a run signal going to it now! Thank you.

I have two MB_MASTER FB's, one for sending the run and another for sending the speed reference, the second one is generating an error code of 8080. Is there anything I may be doing wrong, I've got the second one being requested by the completion flag of the first one and latching with the 'busy' flag to hold the request until complete.

Just a quick update, I was using different instance data blocks, I'm now using the same for both MB_MASTER blocks and it now works perfectly.

Thanks a lot for your help!

aandjsam said:

Just a quick update, I was using different instance data blocks, I'm now using the same for both MB_MASTER blocks and it now works perfectly.

Thanks a lot for your help!

Click to expand...

Good news all around then!
Glad you got it going.