Function Code 04H (Read Actual Values) - GE Multilin 850 Communications Manual

FUNCTION CODE 04H (READ ACTUAL VALUES)

Function Code 04H (Read Actual Values)
11-4
ASE 2000 V2 Example
--> 00 00 00 00 00 06 FE 03 4A 8A 00 04
--> 00 00 00 00 00 0B FE 03 08 00 00 04 B0 00 00 00 64
Modbus Implementation: Read Input Registers
8 Series relay Implementation: Read Actual Values
For the 8 Series relay implementation of Modbus, the 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 8 Series relay 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 11-3: Master Packet Format for Function Code 04H
MASTER TRANSMISSION
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS
NUMBER OF ACTUAL VALUES
CRC (low, high)
Table 11-4: Slave Packet Format for Function Code 04H
SLAVE RESPONSE
SLAVE ADDRESS
FUNCTION CODE
BYTE COUNT
DATA 1
DATA 2
CRC (low, high)
ASE 2000 V2 Example
--> 00 00 00 00 00 06 FE 04 05 95 00 02
--> 00 00 00 00 00 07 FE 04 04 00 00 27 0F
BYTES EXAMPLE
1 FE
1 04
2 05 95
2 00 02
2 75 24
BYTES EXAMPLE
1 FE
1 04
1 04
2 00 00
2 27 0F
2 AF 7F
8 SERIES PROTECTIVE RELAY PLATFORM – COMMUNICATIONS GUIDE
CHAPTER 11: MODBUS PROTOCOL
DESCRIPTION
message for slave 254
read registers
data starting at 0595
2 registers = 4 bytes total
CRC error code
DESCRIPTION
message from slave 254
read registers
2 register = 4 bytes total
value in address 0595 (32-bit)
CRC error code