Rockwell Automation Publication 5069-UM003A-EN-P - May 2018 97
Master Command List Appendix B
The use of slave address 00 (Broadcast Mode) forces all attached slaves to
modify the desired coil.
The following example is a request to slave number 11 to turn ON coil 0173.
Response
The normal response to the Command Request is to retransmit the message as
received after the coil state has been altered.
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).
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".
TIP Functions 5, 6, 15, and 16 are the only messages that are recognized as valid
for broadcast.
TIP This is the structure of the message being sent out to the Modbus network.
The following byte values are in hexadecimal display.
Node Address Function Code Data Start Bit High Data Start Bit Low Number of Bits High Number of Bits Low Error Check Field
(2 bytes)
0B 05 00 AC FF 00 CRC
Node Address Function Code Data Coil Bit High Data Coil Bit Low Data On/Off Data Error Check Field
(2 bytes)
0B 05 00 AC FF 00 CRC
IMPORTANT The Modbus protocol excludes standard functions for testing or changing the
DISABLE state of discrete inputs or outputs. Where applicable, this can be
accomplished via device-specific Program commands (In ProSoft products,
this is only accomplished through Ladder Logic programming).
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