GE Industrial Solutions EntelliPro ES - Manual (Page 145)

4.8 EP OS MOTOR MANAGEMENT SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: COMMUNICATION
4.1.10 EntelliPro ES Function Code
The following sections describe the Modbus function code supported by the EntelliPro ES.
4.1.10.1 Function code 03H
For the EntelliPro ES implementation of Modbus, this function code can be used to read any setpoints (“holding
registers”). Holding registers are 16 bit (two byte) values transmitted high order byte first . Thus all EntelliPro ES Setpoints
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 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 II to respond with 3 registers starting at address 006B. For this example the
register data in these addresses is as follows:
Address Data
0002 0001
0003 0000
0004 0012
The master/slave packets have the following format:
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 006B
NUMBER OF SETPOINT 2 00 03 3 registers = 6 bytes total
CRC 2 78 87 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 1 (see definition above) 2 02 2B value in address 006B
DATA 2 (see definition above) 2 00 00 value in address 006C
DATA 3 (see definition above) 2 00 64 value in address 006D
CRC 2 54 83 CRC error code
Table 4-2: Master/Slave Packet Format For Function Code 03H