ProSoft MVI69E-MBS - Preset Single Register (Function Code 06)

Reference MVI69E-MBS ♦ CompactLogix Platform
User Manual Modbus Serial Enhanced Communication Module
Page 112 of 154 ProSoft Technology, Inc.
June 28, 2017
Coils that are reprogrammed in the controller logic program are not automatically
cleared upon power up. Thus, if such a coil is set ON by function Code 5 and
(even months later), an output is connected to that coil, the output is "hot".
7.2.9 Preset Single Register (Function Code 06)
Query
This Function Code allows you to modify the contents of a Modbus 4x range in
the slave. This writes to a single register only. Any holding register that exists
within the controller can have its contents changed by this message. However,
because the controller is actively scanning, it also can alter the content of any
holding register at any time. The values are provided in binary up to the
maximum capacity of the controller. Unused high order bits must be set to zero.
When used with slave address zero (Broadcast mode), all slave controllers load
the specified register with the contents specified.
Note Functions 5, 6, 15, and 16 are the only messages that are recognized as valid for broadcast.
Note: This is the structure of the message being sent out to the Modbus network. The byte values
below are in hexadecimal display.
The example below is a request to write the value ‘3’ to register 40002 in slave
11.
Node
Address
Function
Code
Data Start Bit
High
Data Start
Bit Low
Preset Data
Register High
Preset Data
Register Low
Error Check
Field (2 bytes)
0B
06
00
01
00
03
CRC
Response
The response to a preset single register request is to re-transmit the query
message after the register has been altered.
Node
Address
Function
Code
Data Register
High
Data Register
Low
Preset Data
Register High
Preset Data
Register Low
Error Check
Field (2 bytes)
0B
06
00
01
00
03
CRC