Preset single register (function code 06) – ProSoft Technology MVI69L-MBS User Manual

Page 112

Reference

MVI69L-MBS ♦ CompactLogix Platform

User Manual

Communication Module

Page 112 of 154

ProSoft Technology, Inc.

January 6, 2014

Node
Address

Function
Code

Data Coil Point
High

Data Coil Point
Low

Data On/
Off

Data Error Check

Field (2 bytes)

CRC

The forcing of a coil via Modbus function 5 is accomplished regardless of
whether the addressed coil is disabled or not (In ProSoft products, the coil is only
affected if the necessary ladder logic is implemented).

Note: The Modbus protocol does not include standard functions for testing or changing the
DISABLE state of discrete inputs or outputs. Where applicable, this may be accomplished via

device specific Program commands (In ProSoft products, this is only accomplished through ladder

logic programming).

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".

7.2.7 Preset Single Register (Function Code 06)

Query
This Function Code allows the user 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 loads
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.

e example below is a request to write the value ‘3’ to register 40002 in slave

11.

Node

Address

Function

Code

Data Start

Point High

Data Start

Point Low

Preset Data

Register

High

Preset Data

Register

Low

Error Check

Field (2 bytes)

CRC