ProSoft Technology 5202-DFNT-MCM4 - Manual (Page 62)

MCM ♦ ProLinx Gateway Reference
Modbus Master/Slave Driver Manual
Page 62 of 80
ProSoft Technology, Inc.
October 16, 2009
8.1.5 Force Single Coil (Function Code 05)
Query
This message forces a single coil 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) will set the coil ON
and the value zero will turn it OFF; all other values are illegal and will not affect
that coil.
The use of Slave address 00 (Broadcast Mode) will force all attached Slaves to
modify the desired coil.
Note: Functions 5, 6, 15, and 16 are the only messages that will be recognized as valid for
broadcast.
The example below is a request to Slave number 11 to turn ON coil 0173.
Adr Func Data Coil # Hi Data Coil # Lo Data On/off Ind Data Error Check Field
11 05 00 AC FF 00 CRC
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
11 05 00 AC FF 00 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".