Buffer Deadlock; The Status Byte; Requesting Service - Quantum Data 801GC, 801GF, 801GX Owner's And Programmer's Manual

available) bit in the Status Byte register is set. This
varies slightly from the 488.2 standard in that the
MAV bit will only be set when at least one com-
plete response message is present in the output queue.
A complete response message consists of response
message text and a message terminator (NL).

Buffer Deadlock

Buffer deadlock is occurs when the 801G* tries to
put a response message in the output queue, the
output queue is full, and the controller is held off
while sending a new message because the input buffer
is full. If deadlock occurs, the 801G* will clear its
output queue, set the query error (QYE) bit in the
Event Status register and proceed to parse incom-
ing messages. If any additional queries are requested
while in deadlock, those response messages will be
discarded.
The 801G* will clear the buffer deadlock when it
finishes parsing the current command/query. The
QYE bit will remain set until read with the *ESR?
query or cleared with the *CLS common command.

The Status Byte

The Status Byte used by the 801G* is the same as
that defined by the IEEE-488.2 standard and does
not use any other bits of the Status Byte. The Status
Byte is one part of a complete status reporting sys-
tem shown on the next set of facing pages. The Sta-
tus Byte is read by using the serial poll feature of
your controller.

Requesting Service

The GPIB provides a method for any device to in-
terrupt the controller-in-charge and request servic-
ing of a condition. This service request function is
handled with the Status Byte. When the RQS bit of
the Status Byte is true, the 801G* is requesting ser-
vice from the controller. There are many conditions
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