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9.0
MODBUS Protocol
Both of the RS232 port on the front panel and the RS485 port on the rear terminals use MODBUS
RTU protocol.
The RS232 front panel port is fixed to 38400bps, even parity, 1 stop bit, relay address 1.
The RS485 rear port communication setting is set by the COMMUNICATION Menu from the front
panel.
9.1 MODBUS Functions
The MODBUS functions described below are used:
0x03/0x04 Read Input/Holding Registers
These 2 commands have the same function
Request
Communication address
1 byte
0* to 255
Function code
1 byte
0x03/0x04
Starting Address
2 bytes
0x0000 to 0xFFFF
Quantity of Registers
2 bytes
0x0001 to 0x007d (N)
CRC
2 bytes
2 bytes CRC
Response
Communication address
1 byte
1 to 255
Function code
1 byte
0x03/0x04
Byte count
1 bytes
2 X N
Quantity of Registers
N X 2 bytes
Value
CRC
2 bytes
2 bytes CRC
Error
communication address
1 byte
1 to 255
Error code
1 byte
0x83/0x84
Exception code
1 bytes
0x01 or 02 or 03 or 04
CRC
2 bytes
2 bytes CRC
0x06 Write Single Register
Request
Communication address
1 byte
0* to 255
Function code
1 byte
0x06
Register Address
2 bytes
0x0000 to 0xFFFF
Register value
2 bytes
Value
CRC
2 bytes
2 bytes CRC
Response
Communication address
1 byte
1 to 255
Function code
1 byte
0x06
Register value
2 bytes
value
CRC
2 bytes
2 bytes CRC
Error
Communication address
1 byte
1 to 255
Error code
1 byte
0x86
Exception code
1 bytes
0x01 or 02 or 03 or 04
CRC
2 bytes
2 bytes CRC