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Revision 2.2b
Protocol identifier (2 Bytes): 0x0000
Length (2 Bytes): 0x0006
Unit identifier (1 Byte): 0xff
Modbus:
Function code (1 Byte): 0x01 (read coils)
Starting address (2 Bytes): 0x0000 (0x0000 ~ 0x0003)
Quantity of coils (2 Bytes): 0x0002 (0x0001 ~ 0x0004)
Character String Example:
char read_coils_mb_request[] ={0x00, 0x01, 0x00, 0x00, 0x00, 0x06, 0xff, 0x01, 0x00, 0x00,
0x00, 0x02 };
Response
Modbus/TCP:
Transaction identifier (2 Bytes): 0x0001
Protocol identifier (2 Bytes): 0x0000
Length (2 Bytes): 0x0004
Unit identifier (1 Byte): 0xff
Modbus:
Function code (1 Byte): 0x01 (Read coils)
Byte count (1 Byte): 0x01
Coil status (1 Byte): 0x00 to 0x0F (see chart below)
Data Byte (hex)
LS Data Bits (binary)
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
0x08
0x009
0x0A
0x0B
0x0C
0x0D
0x0E
0x0F
Modbus Error:
Function code (1 Byte): 0x81
Exception code (1 Byte): 0x01 or 0x02
Exception codes:
0x01 - Function code not supported
Xytronix Research & Design, Inc.
Relay 4 State
0000
off
0001
off
0010
off
0011
off
0100
off
0101
off
0110
off
0111
off
1000
on
1001
on
1010
on
1011
on
1100
on
1101
on
1110
on
1111
on
WebRelay-Quad
Relay 3 State
Relay 2 State
off
off
off
off
off
on
off
on
on
off
on
off
on
on
on
on
off
off
off
off
off
on
off
on
on
off
on
off
on
on
on
on
Users Manual
TM
Relay1 State
off
on
off
on
off
on
off
on
off
on
off
on
off
on
off
on
page 28
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