User manual

4 Modbus RTU MN744
Write Coils
(Function Code 15)
This function code is used to force each coil in a sequence of coils to either ON or OFF in a remote device. The
Request PDU specifies the coil references to be forced. Coils are addressed starting at zero. Therefore, coil 1 is
addressed as 0.
The requested ON/OFF states are specified by contents of the request data field. A logical `1' in a bit position of
the field requests the corresponding output to be ON. A logical `0' requests it to be OFF. The normal response
returns the function code, starting address, and quantity of coils forced.
Request PDU
Function Code 1 Byte 0x0F
Starting Address 2 Bytes 0x0000 to 0xFFFF
Quantity of Outputs 2 Bytes 0x0001 to 0x7B0
Byte Count 1 Byte N*
Outputs Value N* x 1 Byte
*N = Quantity of outputs/8, if the remainder is different of 0⇒ N=N+1
Response PDU
Function Code 1 Byte 0x01
Starting Address 2 Bytes 0x0000 to 0xFFFF
Quantity of Outputs 2 Bytes 0x0001 (0x7B0)
Error
Error Code 1 Bytes 0x8F
Exception Code 1 Bytes 01 or 02 or 03 or 04
Example of a request to write a series of 10 coils starting at coil 20:
Request Response
Field Name (Hex) Field Name (Hex)
Function 0F Function 0F
Starting Address Hi 00 Byte Count 00
Starting Address Low 13 Output Status 27-20 13
Quantity of Outputs Hi 00 Output Status 35-28 00
Quantity of Outputs Lo 0A Output Status 38-36 0A
Byte Count 02
Outputs Value Hi CD
Outputs Value Lo 01
The request data contents are two bytes: CD 01 hex (1100 1101 0000 0001 binary).
The binary bits correspond to the outputs in the following way:
Bit: 1 1 0 0 1 1 0 1 0 0 0 0 0 0 0 1
Output: 27 26 25 24 23 22 21 20 - - - - - - 29 28
The first byte transmitted (CD hex) addresses outputs 27-20, with the least significant bit addressing the lowest
output (20) in this set.
The next byte transmitted (01 hex) addresses outputs 29-28, with the least significant bit addressing the lowest
output (28) in this set.
Unused bits in the last data byte should be zero-filled.