Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT fault ADS 1797: Parameter size not correct (0x705, ADSERR_DEVICE_INVALIDSIZE)
Beckhoff: parameter size not correct. The length sent with an ADS read or write does not match what the server expects for that symbol, index group/offset or service.
Diagnose this with AI
Try Free PLC Fault Diagnostic Upload a keypad photo, the fault history or a parameter export from your Beckhoff TwinCAT 3 (XAR/XAE) with EtherCAT. InduQT compares the evidence and suggests the next useful checks.
When it happens
- On ADS read/write from an HMI, SCADA or ADSREAD/ADSWRITE
- After a PLC data type was changed but the client was not updated
Likely causes and checks
1Variable data type changed in the PLC (e.g. INT to DINT, array or STRING length)
- Points to it
- Error started after a PLC download; only some tags fail.
- Check
- Compare the client’s length with SIZEOF of the PLC variable in the current project.
2Client computes the length wrongly (packing/alignment of structures, STRING terminator)
- Points to it
- Structure reads fail while single variables work.
- Check
- Compare the structure layout and pack mode in the PLC with the client definition.
Telling it apart
- ADS 1808 means the symbol name was not found at all; 1797 means it was found but the size is wrong.
- ADS 1809 (invalid symbol version) appears after an online change invalidated a handle; Beckhoff: create a new handle.
Evidence to collect
- Client tag definitions (name, type, length)
- PLC variable declaration and data type at the current version
- Date of the last PLC download or online change
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