MVI56E-MNETC/MNETCXT ♦ ControlLogix Platform Reference
Modbus TCP/IP Client Enhanced Communication Module - Client/Server User Manual
ProSoft Technology, Inc. Page 141 of 172
September 20, 2018
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Field (2 bytes)
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".
5.4.7 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.
Preset Data
Register High
Error Check
Field (2 bytes)
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