Beckhoff TwinCAT 3 ADS Error 1793: Service Not Supported, what to check?
I'm getting an ADS Error 1793 (0x701) "Service Not Supported" on my TwinCAT 3 runtime. This happens when the client tries to read/write to the PLC. What should I check first?
ADS Error 1793 (0x701) indicates that the addressed ADS device received a request but does not support the specific command or index group. This differs from other ADS errors like 1794/1795, where the service exists but the address is invalid, or ADS 6, where no server responds at all. The server is responding, but it's refusing the service.
Likely causes and checks
1Request sent to the wrong AMS port
- Points to it
- The client might be addressing a port intended for NC, I/O, or system services with a PLC symbol service request, or vice versa. The server receives the request but cannot fulfill it on that specific port.
- Check
- Compare the port used in the request with the standard AMS port table: 851 for PLC, 500 for NC, 300 for I/O, and 10000 for system services.
2Index group or service not available on this TwinCAT version or device
- Points to it
- The specific index group or service requested might not be implemented or supported by the current TwinCAT version or the target device's runtime. This can happen if the target has an older or different runtime compared to where the client was developed or tested.
- Check
- Verify the index group against the device specification in the ADS Basics documentation and confirm the target's TwinCAT build version.
Next check: Start by verifying that the client request is directed to the correct AMS port for the intended service (e.g., PLC services to port 851).
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