Fluke 8840A - Understanding Service Requests; The Serial Poll Register

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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