Modbus data having CRC error CRC16=0xe6.

P

Thread Starter

PT

Hi all,

We have a site where we are interfacing Chiller data over Modbus RTU. We have connected all 4 chillers over RS-485 to convertor RS485to232. We are getting all 4 chiller in Modcan32 tool but in our SCADA we are only getting 3 Chillers and chiller 4 is giving CRC error CRC16=0xe6. We even checked the serial settings in Modscan and our SCADA system is all matching. Due to CRC error the device is getting time out. Please advice if this can be our SCADA problem or Chiller problem. Any help highly appreciated.

Regards
PT
 
S
Sounds like your SCADA may have a bug in it's CRC implementation.

Capture the request packet, and calculate the CRC manually and compare to see if the one calculated by the SCADA is correct or not.

Try a different request from the SCADA to the fourth chiller. A write, or a read but of different register addresses, something that will change the rest of the packet and therefore change the CRC, and see if it comes up right suddenly.

Try a different baud rate.
 
One thing that comes to mind is a spur or stub connection to the problematic slave that could cause a reflection whose 'noise' could alter a bit or two that the CRC picks up.

But that would only be a possibility if Modscan connects differently than the SCADA connects. If both connect the same way through the same converter, there'd be no reason for one to see anything different than the other because either is using data on the CPU/bus side of the PC serial port (unless the SCADA has a bug [how likely is that, if 3 of 4 slave nodes report OK?].

Did you use the same 485/232 converter with Modscan32 as with the SCADA? Did Modscan run on the same PC as the SCADA? Did both Modscan and SCADA tie into the multidrop 485 line at the same point?
 
We are using Modscan and SCADA on same PC. The RS-485 is multi-drop and in Modscan all 4 chillers are giving data but in SCADA chiller 4 is not giving data as it is giving CRCerror. As we can monitor in Modscan so I do not think there is problem in cable or in the modbus device. We will see if from SCADA we can make any changes to avoid CRC error.
 
B
We recently had an CRC issue with some scales we were trying to integrate for a client from Modbus to PROFIBUS. Turned out to be the communications baud rate (not any CRC calculation error related to Modbus communications). Try dropping your baud rate to see if that helps. When we dropped to 2400 bit per second between our MODBUS Master and Slave we had 100% health comms. Seemed the device (Scale) couldn't handle faster comms.
 
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