ProSoft Technology MVI69E-MBTCP User Manual

Page 116

Reference

MVI69E-MBTCP ♦ CompactLogix Platform

User Manual

Modbus TCP/IP Enhanced Communication Module

Page 116 of 150

ProSoft Technology, Inc.

May 20, 2015

Response
The normal response to the Command Request is to re-transmit the message as
received after the coil state has been altered.

Node
Address

Function
Code

Data Coil Bit
High

Data Coil Bit
Low

Data On/Off

Data

Error Check
Field (2 bytes)

CRC

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

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".

7.2.9 Preset Single Register (Function Code 06)

Query
This Function Code allows you to modify the contents of a Modbus 4x range in
the server. 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 server address zero (Broadcast mode), all server 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 server
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)

CRC