Serial Polling - Keithley 775A Instruction Manual

I^ograisiming
Exampls—
Type
in the following statement
into
the
HP-85 keyboard:
REMOTE 723
Place the instrument
in
the one-shot on
GET
bri,gger
mode
with
the foilovving
statement;
OUTPUT 723;
•
'SOX'
'
When
the
END
LINE
key
is
pressed, the
GATE LED
will
stop
Hashing and
the
HOLD
LED
will light
indicating the
instrument
is
waiting
for a trigger.
The
instrument
may
be
triggered
to
take
a single
reading
with
the
foiiowing statement:
TRIGGER 723
The
GArH LSD
w^lil
flash
once, indicating
ihat
one
reading
has
been
processed.
NOTE
The Model
775
will
also re.spond
to
GET
without
addressing.
This
command
is
sent with the foliow-
ng
HF-85
statement:
TRIGGER
7.
NOTE
The Model
775
will
open
the gate and complete
a
reading,
only
if
a
signal
is
applied
to
the input
and
H
proper
trigger level
has
been
set.
The
preceding
examples use device-dependent command,?
to
place the instrument
in the
appropriate
trigger
m.odes.
These
commands
are covered
in detail
in
paragraph
3,10.
3.9.8
Serial
PoiHng (SPE, SPD)
The
serial
polling
sequence
is
used
to
obtain the
Model
775
.status
byte. Usually- the serial polling
sequence
is
used
to
determine
which
of several
devices has requested
service
over the
SRQ
line.
However, the
serial polling
.se-
quence
may
be used
at
any
time
to
obtain the
status
byte
from
the
Model
775
for
more
information
on
status
byte
format,
refer to
paragraph
3.10.15,
The
.seri?4l
polling
sequence
is.
conducted
as follows;
1,
The
controller
sets
the
ATN
line true,
2.
The SPE
(Serial Poll
Enable)
command
is
placed
on
the
bu.s
by
the
controller.
3.
The Model
775
is
addressed
to
talk,
4.
The
controller
sets
ATN
false.
5.
The
instrument then
places
its
Status byte
on
the
bus
to
be read by
the controller.
6.
The
controller then sets the
ATN
line
low and
places
SPD
(Serial Poll
Disable) on
the
bus
to
end
the
serial
polling sequence.
Steps
3
through
5
may
be repeated
for
other instruments
on
the
bus
by using the correct
talk
address
for
each
in-
strument.
ATN
must be
true
when
the
talk
address
is
transmitted
and
false
when
the
status
byte
is
read,
Prograinrning
Example—
The HP-85
SPOIL
statement
automatically
performs
the
serial polling
sequence. To
demonstrate
serial
polling,
momentarily
powerdown
the
Mode!
775 and
enter the following
statements
into
the
HP-85
keyboard;
REMOTE
723
G^SPOLL 723
DISP
3
When END
LINE
is
pressed the
second
time, the
computer
performs
the
serial
polling
sequence.
When
END
LINE
is
pressed
the
last
time, the status byte value
is
displayed
on
the CRT, Paragraph
3.10.15
covers the
status byte
for-
mat
in detail,
3.10
DEVICE-DEPENDENT
COMMAND
PROGRAMMING
IEEE-488 device-dependent
commandvS
are sent
to
the
Model
775
to
control various operating
modes
sucli as
function, trigger
levels,,
gate time,
filter
and
data format.
Each
command
is
made up
of
an ASCII alpha
character
followed by one
of
more numbers
designating
specific
parameters,
For
example, a function
is
programmed
by sen-
ding an ASCII
"F" followed by
numbers
representing
the
function,
The IEEE bus
treats
device-dependent
com-
mands
as data
in
that
ATN
is
high
when
the
commands
are transmitted,
A
number
of
commands may
be
grouped
together
in
one
string.
The Model
775
will ignore
all
nonprintable ASCII
characters
(00
HEX
through
IF
HEX) and
space
character
(20
HEX)
will
be
ignored.
A command
string
is
terminated
by an ASCII "X"
character
which
tells
the Instrument
to
execute
the
command
string.