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Chapter 3      Software Overview

NI-VXI User Manual

3-10

© National Instruments Corporation

until the transfer is complete or a timeout occurs. This support also
keeps a word serial device which is not responding from “hanging” on
the local CPU.

The following paragraphs describe the Commander Word Serial,
Longword Serial, and Extended Longword Serial Protocol functions.
The descriptions are grouped by functionality and are presented at a
functional level describing the operation of each of the functions.

WSabort

 aborts the Commander Word Serial operation(s) in progress

with a particular device. This function does not perform any Word
Serial transfers. Instead, it aborts any Word Serial operation already in
progress. The abortop parameter specifies the type of abort to perform.
The 

ForcedAbort

 operation aborts read, write, and trigger operations

with the specified device. The 

UnSupCom

 operation performs an

Unsupported Command abort of the current Word Serial, Longword
Serial, or Extended Longword Serial command in progress. The

UnSupCom

 operation is called when an Unrecognized Command Event

is received by 

DefaultSignalHandler

.

WSclr

 sends the Word Serial Clear command to a message-based

Servant. The Clear command clears any pending protocol error on the
receiving device. The ERR* bit is ignored during the transfer. The WR
bit is polled until asserted after the Clear command is sent to verify that
the command executed properly.

WScmd

 sends a Word Serial command or query to a message-based

Servant. It polls the WR bit before sending the command, and polls the
RR bit before reading the response (if applicable) from the Data Low
register. 

WScmd

 polls the WR bit after either sending the command (for

a command) or reading the response (for a query), to guarantee that no
protocol errors occurred during the transfer. Under the VXIbus
specification, the ERR* bit can be asserted at any time prior to
reasserting the WR bit. Do not use this function to send the Word
Serial commands Byte Available (BAV), Byte Request (BREQ),
Trigger, or Clear. All of these Word Serial commands require different
Response register polling techniques.