HP 54501A Programming Reference Manual page 76

Parallel Poll Parallel poll
is
a
controller initiated operation which is
used to obtain
information from
several devices simultaneously.
When
a
controller
initiates
a
Parallel Poll, each
device returns
a
Status Bit via one
of the
DIO
data
lines. Device
DIO
assignments are made by the controller using the
PPC (Parallel
Poll Configure) sequence. Devices respond either
individually,
each on
a
separate
DIO line; collectively on
a
single DIO
line;
or any combination of
these two
ways.
When
responding collectively,
the
result
is
a
logical AND
(True High)
or
a
logical OR
(True Low) of the
groups
of the
status bits.
Figure 3-32
shows
the Parallel Poll
Data
Structure.
The
summary bit is
sent
in response to
a
Parallel Poll. This summary bit is
the
"ist" (Individual
Status) local message.
The
Parallel Poll Enable Register determines which
events
are
summarized
in the individual
status local
register.
The
*PRE (Parallel
Poll Register Enable) command
is
used to write to the enable register and
the
*PRE?
query
is used to read the register.
The
*IST? query
can be
used to
read the
"ist"
without doing
a
parallel poll.
Message Communication and System Functions
HP 54501A
3-34
Programming