MVI69E-MBS ♦ CompactLogix Platform Reference
Modbus Serial Enhanced Communication Module User Manual
ProSoft Technology, Inc. Page 111 of 154
June 28, 2017
7.2.8 Force Single Coil (Function Code 05)
Query
This Function Code forces a single coil (Modbus 0x range) either ON or OFF.
Any coil that exists within the controller can be forced to either state (ON or
OFF). However, because the controller is actively scanning, unless the coil is
disabled, the controller can also alter the state of the coil. Coils are numbered
from zero (coil 0001 = zero, coil 0002 = one, and so on). The data value 65,280
(FF00 HEX) sets the coil ON and the value zero turns it OFF; all other values are
illegal and do not affect that coil.
The use of slave address 00 (Broadcast Mode) forces all attached slaves to
modify the desired coil.
Note: Functions 5, 6, 15, and 16 are the only messages that are recognized as valid for broadcast.
The example below is a request to slave number 11 to turn ON coil 0173.
Note: This is the structure of the message being sent out to the Modbus network. The byte values
below are in hexadecimal display.
Error Check
Field (2 bytes)
Response
The normal response to the Command Request is to re-transmit the message as
received after the coil state has been altered.
Error Check
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).
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