Remote Programming
OUTPUT
DATA
Example Explanation This means that an error message always overrides
numeric
data,
but status data is sent even in the pr&ce
+1.0071E+21
CR
LF
ERROR 71: Syntax error in
of an error. However, the status
data
does not
clear!
the
device-dependent command error messagt; the error message
is
sent the next the
string. numeric
data
is requested.
As
with local operation, none of the errors are latching
except for ERROR
31.
If the
mA
DC or
mA
AC function
is requested while the
FRONT/REAR
switch is
in
the
REAR
position, ERROR 31 will persist until the switch is
set to FRONT or another function is selected.
To check for an error condition, test whether the output
buffer
data
is
greater than or
equal
to +1E+21,
or
test the
Any
Error bit (bit
6)
in the serial poll register.
3-47.
Status
Data
349.
SERVICE REQUESTS
Service reQuekts let bus instruments get the attention 08 the
system contrdller. The requests &re sent over the SRQ Pne
(one of the IEEE-488 bus lines). If more than one insitru-
ment on the bus is capable of sending service requests, the
controller
cad
learn which one
made
the request by twng
a
serial
poll. Each device (including the
8840A)
respeinds
to
the poll by sending the contents of its serial
Pl1
register. The
serial
poll register indicates whether or not
the device reQtested service,
and
if so, the reason for the
request.
The 8840A may
be
programmed to make a service request
G5, G6, G79
G8 mmmands- The data is formatted as
by
a
due
for the %&ice
(~RQ
shown in Figure 3-2, and is interpreted in Table 3-1.
with
PI
me
SRQ
maJk
worb
by
Exam~ls of status data
can
be
found in the -@on of
monitoring Qe
serial
poll register, which in turn monitors
the Get commands.
various conditions in the 8840A.
The user-defined message loaded by the G3 command
Service requekts may also
be
initiated using the front pbel
consists of 16 characters plus terminators. The
SRQ
mask
SRQ button if it
has
been enabled by the SRQ
mask.
loaded by the G1 command consists of two integers plus
terminators. All other
status
data
ex-
G8. is alwavs a
3-50.
The
&rial
Poll Register
four-digit integer plus terminators. Tjle
LF
The serial poll register
is
a binary-emmded register which
(~i~~
~~~d)
and
CR
(carriage
each
add
an
contains eight bits,
as
illustrated in Figure
3-9.
The hn-
character when enabled.
troller
can
read the 8840A
serial
poll register at any mime
by taking a serial poll. Because' serial poll register
data
is
loaded
directly onto the
bus
(instead of being loaded into
?be
8840A
begiar
data a
leading the output er
first),
readiqg the serial poll register
one (1) or a one and a zero (10).
Prevents
the
leave
&ta
in
the output buffer intact.
controller from suppressing
any
leading
zeros
present
in
the 8840A5s output string: It
&so
gives a uniform four-
The eight bits of
the
serial poll register are described in
character length to
all
instrument configuration
data.
Figure 3-9. Note that the SRQ mask uses bits
1
thou@
6
to set bit
7
(ihe RQS bit).
When
the RQS
bit
is
set
{rue,
Status
data
from the Get (30mmands reflects the status of
88mA
sets
the SRQ line true, which generaw a
the
at
the time the commnd
is
at
its
place
senrice reque$t.
A
bit
is
mnsideted true when it
is
set t'o
1.
in the input command string.
Bit
1
(We lowest-order bit)
is
set true on overr4ge.
When overrange occurs, the output
buffer
is loqded
348.
Output
Priority
=9.99999E+9 (and a suffix, if enabled).
Since only one output string is allowed per input command
string, the 8840A gives priority to some types of data over
others.
An
input command string may
call
for more than
one output string. (For example, an input string may
contain
a
Get command but
also
cause
an
error message.)
However, the output buffer
is
loaded
with
only one output
string. That string
is
selected according to the following
priority:
1.
Status
data
(from GO, GI, G3, G4, G5, G6, G7, or
w
Bit
2
is not
used.
It is always
set
to
0.
Bit 3
is
set true when the
front
panel SRQ button is
pre-
Bit 4,
Oal
Step Complete, is set true when a tore
command is completed in the calibration proc&re.
Bit
5,
Dqta
Available, is set true every time the oqtput
buffer
is
loaded, regardless of the kind of output
!data
(includirig error messages). This bit is cleared (set to
0)
when
any
new bus input
occurs,
when the output
buffer
is
read, or when
an
external trigger occurs.
2.
Error messages (if an error exists)
Bit
6,
My Error, is set true whenever an error
cqndi-
tion occurs. At the same time that bit
6
is set true, the
3. Numeric
data
(from G2 or a trigger)
output buffer is loaded with
an
error message.
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