2 Protocol description
18
2.9 Error processing
Error codes The following error codes exist:
1invalid function
2 invalid parameter address or too many words
are to be read or written
8 write access to parameter denied
Response in
the
event of an
error
0x80 is used to set the function code to its OR status, i.e. the MSB (most
significant bit) is set to 1.
Example Data request:
Response (with error code 2):
Special cases The slave not responding can have the following causes:
- the baud rate and/or data format of Master and Slave are not compatible
- the device address used does not coincide with that of the slave address
- the checksum (CRC16) is not correct
- the instruction from the Master is incomplete or over-defined
- The number of words to be read is zero.
In these cases the data request should be transmitted again once the timeout
time (2 s) has elapsed.
Slave
address
Function
XX OR 80h
Error code Checksum
CRC16
1 byte 1 byte 1 byte 2 bytes
01 03 40 00 00 04 CRC16
01 83 02 CRC16
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