Function Code 03H - GE MOTOR MANAGER 2 Instruction Manual

6.2 MODBUS FUNCTIONS
Modbus implementation: Read Holding Registers
MM2 implementation: Read Setpoints and Actual Values
For the MM2 implementation of Modbus, this command can be used to read any setpoints ("holding
registers") or actual values ("input registers"). Holding and input registers are 16 bit (two byte) values
transmitted high order byte first. Thus all MM2 Setpoints and Actual Values are sent as two bytes.
The maximum number of registers that can be read in one transmission is 125. This function code is
identical to function code 04.
The slave response to this function code is the slave address, function code, a count of the number
of data bytes to follow, the data itself and the CRC. Each data item is sent as a two byte number with
the high order byte sent first.
For example, consider a request for slave 17 to respond with 3 registers starting at address 006B.
For this example the register data in these addresses is as follows:
Address
006B
006C
006D
The master/slave packets have the following format:
Table 6–2: MASTER/SLAVE PACKET FORMAT FOR FUNCTION CODE 03H
6
MASTER TRANSMISSION
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS
NUMBER OF SETPOINTS
CRC
SLAVE RESPONSE
SLAVE ADDRESS
FUNCTION CODE
BYTE COUNT
DATA 1 (see definition above)
DATA 2 (see definition above)
DATA 3 (see definition above)
CRC
6-6
Data
022B
0000
0064
BYTES
1
1
2
2
2
BYTES
1
1
1
2
2
2
2
MM2 Motor Manager 2

6.2.2 FUNCTION CODE 03H

EXAMPLE DESCRIPTION
11 message for slave 17
03 read registers
00 6B data starting at 006B
00 03 3 registers = 6 bytes total
76 87 CRC error code
EXAMPLE DESCRIPTION
11 message from slave 17
03 read registers
06 3 registers = 6 bytes
02 2B value in address 006B
00 00 value in address 006C
00 64 value in address 006D
54 83 CRC error code
6 COMMUNICATIONS
GE Power Management