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469 MOTOR MANAGEMENT RELAY – COMMUNICATIONS GUIDE
MODBUS FUNCTIONS
COMMUNICATIONS GUIDE
MESSAGE FORMAT AND EXAMPLE:
Perform a reset on 469 (operation code 1).
Error Responses
When an 469 detects an error other than a CRC error, a response will be sent to the master.
The MSbit of the Function Code byte will be set to 1 (i.e. the function code sent from the
slave will be equal to the function code sent from the master plus 128). The following byte
will be an exception code indicating the type of error that occurred.
Transmissions received from the master with CRC errors will be ignored by the 469.
The slave response to an error (other than CRC error) will be:
SLAVE ADDRESS: 1 byte
FUNCTION CODE: 1 byte (with MSbit set to 1)
EXCEPTION CODE: 1 byte
CRC: 2 bytes
The 469 implements the following exception response codes.
01: ILLEGAL FUNCTION
The function code transmitted is not one of the functions supported by the 469.
02: ILLEGAL DATA ADDRESS
The address referenced in the data field transmitted by the master is not an allowable
address for the 469.
03: ILLEGAL DATA VALUE
The value referenced in the data field transmitted by the master is not within range for the
selected data address.
Master Transmission
Bytes
Example
Description
Slave Address
1
0B
message for slave 11
Function Code
1
10
store multiple setpoint value
Data Starting Address
2
00 80
data starting at 0080h
Number of Setpoints
2
00 02
2 setpoints = 4 bytes total
Byte Count
1
04
4 bytes of data
Command Function
2
00 05
data for address 0080h
Command Operation
2
00 01
data for address 0081h
CRC (low, high)
2
0B D6
computed CRC error code
Slave Response
Bytes
Example
Description
Slave Address
1
0B
message from slave 11
Function Code
1
10
store multiple setpoint value
Data Starting Address
2
00 80
data starting at 0080h
Number of Setpoints
2
00 02
2 setpoints = 4 bytes total
CRC (low, high)
2
40 8A
computed CRC error code
