Supported Modbus Functions; Description; Function Code 03: Read Setpoints - GE 735 Instruction Manual

4.2 SUPPORTED MODBUS FUNCTIONS

4.2 SUPPORTED MODBUS FUNCTIONS
The following functions are supported by the 735/737:
• 03: Read Setpoints
• 04:Read Actual Values
• 05: Execute Operation
• 06: Store Single Setpoint (test/simulation)
• 07: Read Device Status
• 16: Store Multiple Setpoints (test/simulation)
Modbus implementation: Read Holding Registers
735/737 implementation: Read Setpoints
For the Modbus implementation, "holding registers" are equivalent to memory locations reflecting the user switch settings.
Holding registers are 16-bit (two byte) values transmitted high order byte first. Thus all setpoints are sent as two bytes. This
function code allows the master to read setpoints from a slave device.
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The slave response 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 (setpoint) is sent as a two byte number with the high order byte sent first. Note that broadcast mode
is not allowed with this function. The master transmission will be ignored by all slaves if broadcast mode is used with this
function code.
Message Format and Example:
Request slave 11 to respond with 3 setpoints starting at address 0040. For this example the setpoint data is:
ADDRESS DATA
0040 0003
0041 0000
0042 0009
MASTER TRANSMISSION:
SLAVE ADDRESS
FUNCTION CODE
START ADDRESS
NUMBER OF SETPOINTS
CRC
SLAVE RESPONSE:
SLAVE ADDRESS
FUNCTION CODE
BYTE COUNT
DATA #1
DATA #2
DATA #3
CRC
4-4

4.2.2 FUNCTION CODE 03: READ SETPOINTS

BYTES EXAMPLE / DESCRIPTION
1 11 message for slave 11
1 03 read setpoints
2 00 40 data starts at 0040h
2 00 06 3 setpoints = 6 bytes
2 ?? ?? CRC calculated by the master
BYTES EXAMPLE / DESCRIPTION
1 11 response message from slave 11
1 03 read setpoints
1 06 3 setpoints = 6 bytes
2 00 03 setpoints data at 0040h
2 00 00 setpoints data at 0041h
2 00 09 setpoints data at 0042h
2 ?? ?? CRC calculated by the slave
735/737 Feeder Protection Relay
4 MODBUS COMMUNICATIONS

4.2.1 DESCRIPTION

GE Power Management