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8–6 MM3 MOTOR MANAGER 3 – INSTRUCTION MANUAL
SUPPORTED MODBUS FUNCTIONS CHAPTER 8: COMMUNICATIONS
8.2.3 Function Code
03h
Modbus implementation: Read holding registers
MM3 Motor Manager 3 implementation: Read setpoints and actual values
For the MM3 Motor Manager 3 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 MM3 Motor
Manager 3 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:
The master/slave packets have the following format:
8.2.4 Function Code
04h
Modbus implementation: Read input registers
MM3 Motor Manager 3 implementation: Read setpoints and actual values
For the MM3 Motor Manager 3 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 MM3 Motor
Manager 3 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 03.
Address Data
006B 022B
006C 0000
006D 0064
Master transmission Bytes Example Description
Slave address 1 11 message for slave 17
Function code 1 03 read registers
Data starting address 2 00 6B data starting at 006Bh
Number of setpoints 2 00 03 3 registers = 6 bytes total
CRC 2 76 87 computed CRC error code
Slave response Bytes Example Description
Slave address 1 11 message from slave 17
Function code 1 03 read registers
Byte count 1 06 3 registers = 6 bytes
Data word 1 (see definition above) 2 02 2B value in address 006Bh
Data word 2 (see definition above) 2 00 00 value in address 006Ch
Data word 3 (see definition above) 2 00 64 value in address 006Dh
CRC (low, high) 2 54 83 computed CRC error code