GE Industrial Solutions EntelliPro ES - Manual (Page 146)

EP OS MOTOR MANAGEMENT SY STEM – INSTRUCTION MANUAL 4.9
CHAPTER 4: COMMUNICATION
4.1.10.2 Function Code 04H
Modbus Implementation: Read Input Registers
EntelliPro ES implementation: Read Actual Values
For the EntelliPro ES implementation of Modbus, this function code can be used to read any actual values (“input
registers”). Input registers are 16 bit (two byte) values transmitted high order byte first . Thus all EntelliPro ES Actual
Values are sent as two bytes. The maximum number of registers that can be read in one transmission is 125.
The slave response to this function code is the slave address, function code, a count of the 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, request slave 17 to respond with 1 register starting at address 0008. For this example the value in this
register (0008) is 0000.
MASTER TRANSMISSION BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message for slave 17
FUNCTION CODE 1 04 read registers
DATA STARTING ADDRESS 2 00 08 data starting at 0008
NUMBER OF ACTUAL VALUES 2 00 01 1 register = 2 bytes
CRC 2 B2 98 CRC error code
SLAVE RESPONSE BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message from slave 17
FUNCTION CODE 1 04 read registers
BYTE COUNT 1 02 1 register = 2 bytes
DATA (see definition above) 2 00 00 value in address 0008
CRC 2 78 F3 CRC error code
Table 4-3: Master/Slave Packet Format For Function Code 04H