Hp-Ib - HP 54501A Programming Reference Manual

Serial Poll
The
HP 54501A
supports the
IEEE
488.1 serial
poll feature. When
a
serial
poll of the
instrument
is requested, the
RQS
bit
is returned on bit
6
of the status byte.
Using Serial Poll. This
example will show
how to
use
the service request
by
conducting
a
serial
poll of
all instruments on the
bus.
In
this
example,
assume that there are two instruments on the bus; an oscilloscope
at
address 7 and
a
printer at
address
1.
These
address assumptions are
made
throughout this
manual, and
it is also assumed
that we are operating on
Interface Select Code
7.
The program command for
serial
poll using HP BASIC
4.0 is
Stat
=
SPOLL(707). The
address 707
is the address of
the oscilloscope in
this example.
The
command for checking the printer
is
Stat
=
SPOLL(701)
because the address
of that instrument is
01 on bus
address 7.
This command
reads the contents of the HP-IB
Status Register
into the variable called
Stat.
At
that time bit 6
of the variable
Stat can be
tested to
see
if
it is
set
(bit
6
=
1).
The
serial
poll operation
can be
conducted in the following manner.
1.
Enable interrupts on
the bus.
This
allows the controller
to
"see" the
SRQ
line.
2.
If
the
SRQ
line
is
high
(some instrument is requesting service) then
check the instrument
at address
1
to
see
if
bit 6
of
its
status
register is
high.
3. Disable interrupts on the
bus.
Message Communication and System Functions
HP 54501A
3-32
Programming