Table 10-35 Modbus Rtu Data Layer Status Exception Codes - Honeywell UDC3500 Product Manual

Query
Example: Internal slave error reading 2 registers starting at address 1820h from slave at slave address 02.
02 03 18 20 00 02 CRC CRC
Response
Example: Return MSB in Function Code byte set with Slave Device Failure (04) in the data field.
02 83 04 CRC CRC

Table 10-35 Modbus RTU Data Layer Status Exception Codes

Exception
Code
Illegal Function
01
02 Illegal Data Address
03 Illegal Data Value
Slave Device Failure
04
Slave Device Busy
06
07 NAK,
Negative Acknowledge
09 Buffer Overflow
3/07
Modbus Read, Write and Override Parameters plus Exception Codes
Definition
The message received is not an allowable action for
the addressed device.
The address referenced in the function-dependent data
section of the message is not valid in the addressed
device.
The value referenced at the addressed device location
is no within range.
The addressed device has not been able to process a
valid message due to a bad device state.
The addressed device has ejected a message due to a
busy state. Retry later.
The addressed device cannot process the current
message. Issue a PROGRAM POLL to obtain device-
dependent error data.
The data to be returned for the requested number of
registers is greater than the available buffer space.
Function Code 20 only.
UDC3500 Universal Digital Controller Product Manual
Description
435