MVI56E-MCMR ♦ ControlLogix Platform Reference
Modbus Communication Module with Reduced Data Block User Manual
ProSoft Technology, Inc. Page 183 of 223
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".
6.6.7 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 Slave address zero (Broadcast mode) all Slave
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.
Response
The response to a preset single register request is to re-transmit the query
message after the register has been altered.
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