HP 3468A - Page 81

2.
Now
turn
the
3468A
off.
On
the
rear
panel
find
the
bank
of
switches
and
set
switch
3,
Power-on
SRQ,
to
the
up
(1)
position.
When
you
turn
the
3468A
back
on,
the
SRQ
annunciator
should
be
on
in
the
display.
Now
do
a
serial
poll.
The
status
byte
returned
by
the
3468A
shows
a
value
of
193.
This
means
that
bits
7, 6,
and
1
were
true
(128+64+1=193).
Bit
6
is
true
because
of
the
power-on
SROQ
condition.
Bit
7
is
true,
as
in
the
first
step,
because
a
power-on
reset
occurred.
Because
the
Power-on
SRQ
switch
was
“SET”,
when
the
3468A
was
turned
on,
it
sent
the
Service
Request
message
(SRQ).
After
you
do
the
serial
poll,
the
SRO
annunciator
will
turn
off.
3.
Finally,
turn
the
3468A
off
and
return
switch
3
to
the
down
position.
Turn
the
3468A
on,
notice
that
the
SRO
annunciator
is
not
on,
and
send
it
the
message
“MO1”.
MO1
sets
the
SRO
mask
for
the
data
ready
condition.
In
just
a
moment
the
SRQ
annunciator
will
turn
on
in
the
display.
Again
do
a
serial
poll.
The
value
returned
should
again
be
193
(bits
7, 6,
1).
This
time
the
SRQ
occurred
because
the
SRQ
Mask
was
set
for
bit
0,
Data
Ready.
Do
another
Serial
Poll
and
notice
that
the
SRO
annunciator
goes
off
momentarily
until
new
data
is
available.
The
value
returned
from
this
second
Serial
Poll
is
65
because
bit
7
was
cleared
by
the
first
poll.
The
previous
section
on
Service
Request
gave
two
example
programs
demonst-
rating
SRQ
interrupts.
Look
at
the
second
program,
FRONT
PANEL
SRQ.
Change
line
70
to
read:
70
GOTO
60
and
run
the
program.
Line
40
sets
the
SRQ
mask
to
front
panel
SRQ.
Line
1000
performs
a
serial
poll
when,
and
only
when,
an
SRO
condition
occurs
(i.e.,
when
you
press
the
3468A
SRQ
key).
Line
1010
looks
at
bit
4
of
the
Status
Byte
to
verify
that
it
was
the
front
panel
SRO
key
that
caused
the
interrupt.
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