ProSoft Technology PLX3 Series User Manual page 144

MBS Protocol
User Manual
Response
The normal response to the Command Request is to re-transmit the message as
received after the coil state has been altered.
Func Data Coil # Hi
Adr
05 00
11
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".
Preset Single Register (Function Code 06)
Query
Function (06) allows the user to modify the contents of a holding register. 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 will load the specified register with the contents specified.
Note: Functions 5, 6, 15, and 16 are the only messages that will be recognized as valid for
broadcast.
Func Data Start Reg
Adr
Hi
06 00
11
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Data Coil # Lo Data On/ Off
AC FF
Data Start Reg Data #of Regs Hi Data #of Regs Lo
Lo
01 00
Ethernet and Serial Gateways
Data Error Check Field
00 CRC
Error Check Field
03 CRC
ProSoft Technology, Inc.
PLX3x Series
May 26, 2016