Honeywell Experion PKS User Manual page 127

There are two scenarios during which control word could be sent non-atomically to the PROFIBUS.
• A PIOMB is not connected to the PPO output PDC - The engineer or the operator may directly change the
control word bit-by-bit from the DSB display in Control Builder or Station. In such a scenario, these
changes are sent individually and therefore results in incremental control word changes being sent to the
device.
• The DO channels associated with the control word are in separate CMs, they may be on different phases and
have different cycles - This results in partial updates to the control word (bit-by-bit change) being sent to the
device.
See "Data processing" on page 118.
PKW Processing
The PKW processing enables you to process and monitor parameters (write/read). The PKW processing is
applicable only to the PPO types 1, 2, and 5. The DSB uses the same data areas for both read and write requests
for these channels.
The flow of the PKW processing by the DSB is as follows:
1. Identifies the first PDC channel that is associated with a PKW PDC.
2. Updates the PKW section of the output area with the appropriate information.
3. Sends out the PKW data.
4. Reads the PKW input data until the response ID is not 0 (no response).
5. Compares the request Parameter Number with the response Parameter Number to ensure that they are
identical.
6. Sets the channel status based on the response ID.
7. Copies the response value to the requested channel.
8. Identifies the next PDC channel that is associated with a PKW PDC.
9. Repeats step 3 through step 7 for the other PDC channels that are associated with the PKW PDCs one at a
time.
Attention
• The channel status is set to "Bad_NonSpecific" when the response of a PKW read or write is one of the following;
otherwise, the channel status is set to "Good."
– "Task cannot be executed < error number>"(7)
– "No parameter change rights for PKW interface" (8).
• During the processing, if there are any errors encountered on a PKW read or write, the channel status is set to
"Bad" and the processing of the next PKW channel continues.
• Also, if errors specific to PKW area are encountered, these are rectified by handling the response IDs and setting
the channel status as "Bad."
Channel status processing
A short delay of approximately 10 seconds or less is introduced for the DRIVEDSBs while transitioning the
status from "Bad" to "Good." This is to ensure proper behavior of the DSB and also to avoid fluctuating status.
The DRIVEDSB only supports channel-level status for PKW channels. Also, all channels follow the status of
the entire PDC. Therefore, if one channel is bad, all channels will be bad.
Tip
If a PKW channel is bad, it is a result of an error response for that PKW request.
Diagnostics
The extended diagnostic data specifics are not defined for the PROFIdrive specification. However, the
DRIVEDSB actually uses the process data area for alarming.
7 DEVICE SUPPORT BLOCK (DSB)
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