Force Single Coil (Function Code 05) - ProSoft Technology CompactLogix MVI69E-MBS User Manual

MVI69E-MBS ♦ CompactLogix™ Platform
Modbus Serial Enhanced Communication Module

8.2.8 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.
Function
Node
Code
Address
05
0B
Response
The normal response to the Command Request is to re-transmit the message as
received after the coil state has been altered.
Function
Node
Code
Address
05
0B
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".
ProSoft Technology, Inc.
Data Start Bit Data Start Bit
High Low
00 AC
Data Coil Bit Data Coil Bit
High Low
00 AC
Number of Number of
Bits High Bits Low
FF 00
Data On/Off Data
FF 00
Reference
User Manual
Error Check
Field (2 bytes)
CRC
Error Check
Field (2 bytes)
CRC
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