GE Industrial Solutions EntelliGuard TU Trip Units - Manual (Page 61)

DEH-4567B EntelliGuard TU Trip Units: UL/ANSI Models
Serial Communication
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Function Code 03H
For the EntelliGuard Trip Unit 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
EntelliGuard Trip Unit 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 listed below:
Table 8-1: Function Code 03H Example
Address Data
0002 0001
0003 0000
0004 0012
The master/slave packets have the following format:
Table 8-2: Modbus Packet Format for Function Code 03H
Master
Transmission
Bytes Example Description
Slave Address 1 11 message for slave
2
Function Code 1 03 read registers
Data Starting
Address 2 00 6B data starting at
006B
Number of
Setpoints 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
Function Code 04H
Modbus Implementation:
Read Input Registers.
EntelliGuard Trip Unit implementation:
Read Actual Values
For the EntelliGuard Trip Unit 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
EntelliGuard Trip Unit 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.
Table 8-3: Modbus Packet Format for Function Code 04H
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
Function Code 05H
Modbus Implementation:
Force Single Coil
EntelliGuard Trip Unit Implementation:
Execute Operation
This function code allows the master to request an
EntelliGuard Trip Unit to perform specific command
operations.
For example, to request slave 17 to execute operation code
108 (Trip Breaker), we have the following master/slave
packet format: