GE 469 Communications Guide

COMMUNICATIONS GUIDE MODBUS FUNCTIONS
469 MOTOR MANAGEMENT RELAY – COMMUNICATIONS GUIDE 7
Read Setpoints and Actual Values
Modbus implementation: Read Input and Holding Registers
469 Implementation: Read Setpoints and Actual Values
For the 469 implementation of Modbus, these commands can be used to read any setpoint
(“holding registers”) or actual value (“input registers”). Holding and input registers are 16 bit
(two byte) values transmitted high order byte first. Thus all 469 setpoints and actual values
are sent as two bytes. The maximum number of registers that can be read in one
transmission is 125. Function codes 03 and 04 are configured to read setpoints or actual
values interchangeably because some PLCs do not support both function codes.
The slave response to these function codes 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. The CRC is sent as a two byte number
with the low order byte sent first.
MESSAGE FORMAT AND EXAMPLE:
Request slave 11 to respond with 2 registers starting at address 0308. For this example the
register data in these addresses is:
D3: Starter Status Open D8: Assignable Input 3 Open
D4: Emergency Restart Open D9: Assignable Input 4 Closed
D5: Remote Reset Closed Bit Mask (LSB) 0111 0001
Master Transmission Bytes Example Description
Slave Address 1 0B message for slave 11
Function Code 1 02 read digital input status
Starting Digital Input 2 00 01 starting at digital input 1
Number of Digital Inputs 2 00 04 4 digital inputs (inputs 1 to 4)
CRC (low, high) 2 28 A3 computed CRC error code
Slave Response Bytes Example Description
Slave Address 1 0B message from slave 11
Function Code 1 02 read digital input status
Byte Count 1 01 1 byte bit mask
Bit Mask 1 01 bit mask of requested input
CRC (low, high) 2 63 90 computed CRC error code
Address Data
0308 0064
0309 000A
Master Transmission Bytes Example Description
Slave Address 1 0B message for slave 11
Function Code 1 03 read register values
Data Starting Address 2 03 08 data starting at 0308h
Number of Registers 2 00 02 2 registers = 4 bytes total
CRC (low, high) 2 45 27 computed CRC error code

GE 469 Specifications

General

Model	GE 469
Category	Relays
Frequency	50/60 Hz
Protection Functions	Overcurrent
Communication Protocols	Modbus, DNP3, IEC 61850
Display	LCD
Mounting	Panel