Help: Beckhoff profibus master FC3121 with Siemens CP342-5 slave

hosplc

Member
H
Join Date
May 2005
Posts
15
Dose anyone have experience with Beckhoff FC3121 profibus master PCIe card connected to Siemens CP342-5 as a profibus slave?

The data retrieved from S7 PLC is wrong, and keeps fluctuating rapidly.
TwinCAT (TC) config looks OK, and it reports that the slave is OK and has no error.
The slave is in Run mode with green LEDs.
S7 side is believed to be OK as another master from HMS-Anybus retrieved the data correctly.

Tried several versions of TC up to the latest (at the moment) ver. 2.11.2305.
Attached are two graph pics of the two masters showing how the "same" data looks like in each case.

Thanks,
Hos

Bad_Beckhoff.png Good_HMS-Anybus.png
 
The addresses were assigned automatically by TC during the configuration phase.

I'm out right now, when I return home, I can give more details.
 
Can you post screenshots of configuration on PLC and Beckhoff. It is easier to look then without programs.
 
On the S7 / CP342-5 side, you are transferring 128 bytes.
Does that correspond with the number of bytes that are configured in the master ?
It must be the net used no of bytes, last byte no minus the first byte no.

Can you somehow monitor the source DB in the S7 CP in parallel with the target address in the Beckhoff CPU ?
So that you can verify that "12345" in S7 is also "12345" in Beckhoff.
 
The master (as I posted its config) is configured to receive 64 words.
Even though I'm sure that this should not be a problem, I tried a different config to receive 128 bytes. Same result and I confirmed that the words values (in the first config) are parsed into bytes in the second.

There is no Beckhoff CPU. The master is being used to provide the data to a special software for data logging.

I'm in the process of making the suggested monitoring though.
 
I wonder if the data could be offset by 1 or 2 bytes for some reason.

I checked this [high low byte swap] also.
Even if they are swapped, the wrong value should be fixed if it's fixed in the PLC.
Click to expand...
If the bytes are interpreted differently, when the value is changed slightly at the sender you may see some odd "jumps" in the values on the receiving side.
 
JesperMP said:
I wonder if the data could be offset by 1 or 2 bytes for some reason.

If the bytes are interpreted differently, when the value is changed slightly at the sender you may see some odd "jumps" in the values on the receiving side.
Click to expand...




HEX vs BOOL?


I encountered that problem a few years ago when implementing a Beckhoff master with Ethernet-IP-slaves.


Twincat 2 used HEX, Twincat 3 used BOOL (INT) or was visa-versa.
 
Address offset: no
Bytes swapped: yes

Hold on, I'm waiting for detail from the field for a possible fix.
 

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