ProSoft Technology MVI69-MCM User Manual

Page 139

MVI69-MCM ♦ CompactLogix or MicroLogix Platform

Reference

Modbus Communication Module

User Manual

ProSoft Technology, Inc.

Page 139 of 167

March 22, 2011

Response
The normal response to the Command Request is to re-transmit the message as

received after the coil state has been altered.

Adr

Func

Data Coil # Hi

Data Coil # Lo

Data On/ Off

Data

Error Check Field

CRC

The forcing of a coil via MODBUS function 5 will be 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 will be "hot".

5.6.7 Preset Single Register (Function Code 06)

Query
Function (06) allows the user to modify the contents of a holding register. 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 will load the specified register with the contents specified.

Note Functions 5, 6, 15, and 16 are the only messages that will be recognized as valid for
broadcast.

Adr

Func

Data Start Reg
Hi

Data Start Reg
Lo

Data #of Regs Hi Data #of Regs Lo

Error Check Field

CRC