Remote Programming
DEVICE-DEPENDENT
COMMkND
SET
I
I
The suffix status
can
be
read using the
G6
command. The
8840A defaults to YO on power-up and any device-clear
command
(*,
DCL or SDC), unless in talk-only mode.
3-33.
ZO
(Self-Test
Command)
The ZO command initiates the diagnostic self-tests as
does
pressing the front panel SRQ button for 3 seconds. The
8840A then
runs
through the tests
in
sequence. (For a
description of the self-tests, see the Maintenance section.)
If the
8840A detects an enor, an error message is loaded
into the output buffer md displayed on the front panel.
After the last test, the 8840A is reset to the power-up
configuration, and it
begins
taking readings.
It is an error to send the 8840A device-dependent com-
mands during the self-tests. However, the controller
can
still make the 8840A a talker to read the output buffer
during the test, and thus record each error that occurs,
except that only the last of the
digital
self-test errors
can
be
read. After the tests, only the last error is stored in the
output buffer if more than one error occurred.
Error messages are indicated by an exponent of +21. For
more about error messages, see paragraph
3-40.
Since the 8840A is reset
at
the end of the self-tests, the
ZO
command should be the last command in a given com-
mand string. The 8840A will ignore any subsequent com-
mands in the same command string.
When the
self-tests are complete
and
no errors have
occurred,
the serial poll register will have bit 5 (Data
Available) true and bit
6
(Any Error) false.
See
paragraph
3-50 for more about the serial poll register.
3-34.
*
(Device-Clear Command)
The asterisk command
(*)
is a device-dependent message
which resets the 8840A to the power-up default settings
and
clears
all registers and buffers except for the
input
buffer. The remotenocal status remains unchanged.
The
asterisk command performs the following:
1.
Implements the default settings F1, RO,
SO,
TO, DO,
BO,
YO, WO.
I
similar; however,
DCL
and SDC are not identical td the
asterisk command
described
here.
DCL
and SDC are
discussed further in the paragryph on interface m-es.
3-35.
?
(Single-Trigger Command)
I
The Single-Trigger command
(?)
causes
the WA to take
a reading and place the result into the output bufferl To
accept this command, the WA must
be
in
extipnal
trigger mode (selected by the TI,
T2,
T3,
or T4 aom-
mand).
The Single-Trigger command is one of five ways to triper
a reading. (See Figure 3-7.) Of these, only the Siee-
Trigger command
(?)
and the Group Execute Tri er
command
(GET)
are loaded into the input buffer.
p
3-36.
INPUT
SYNTAX
The following paragraphs describe how to construct
groups of commands for the 8840A. A few definition$ are
presented first, followed by a description of how the
MA processes input commqds. Guidelines are
hen
summarized in four syntax rules.
3-37.
Definitions
Output commands: Commands which load
data
into
the output buffer.
The
output commands are: the Get
commands (GO through G8); the Single-Trigger
-
F
mand
(?);
the Continuous Trigger command
(TO),
and
Group Execute Trigger (GET), not to
be
co&sed
with the Get commands.
Input terminator:
An
ASCII control code sent the
controller which tells the 8840A to execute all debice-
dependent commands since the previous termirjator.
Terminators are CR (Carriage Return),
LF
@me
Feed), EOI (End Or Identify), and GET (Group pxe-
cute Trigger).
I
Input command string: One or more device-de4dent
commands followed by a terminator.
2.
Clears the error status register (equivalent to
XO).
3-38.
Input Processing
3.
Zeros the SRQ mask, prohibiting service requests
When the 8840A receives commands from the
(equivalent to NO
PI).
stores them in a 31-character input buffer
as
a
4.
Zeros the numeric entry register (equivalent to NO).
hng of ~kuacter~- Chumnds in the input
executed or checked for syntax until an
5.
Zeros the
serial
poll register.
received or the input buffer becomes
6.
Sets the SRQ line
false.
input terminators are
CR,
LF,
GET
(Group Execute
~Ager), and/or EOI.
I
The asterisk command is executed in its proper turn in a
string, just like any other command, without affecting the
When the
MA
receives
an
input terminator, it ex
contents of the input buffer.
All
commands which precede
lhe pr&cyus comm& in the order in which they were
the asterisk command are performed.
=Pa
received.
As
input characters are processed and exequted,
The asterisk
command
is
useful
to
ensure
that
the
8840A
space is made available in the input buffer for new cliarac-
is initialized to the same state each time a program is
run.
By contrast, the similar interface messages DCL (Device
Clear) and SDC (Selected Device Clear) cause the entire
If
the
input
buffer
the
stops
input buffer to
be
cleared immediately.
characters from the bus until all complete
strings currently in the input bvffer have been execut&. In
DCL, SDC, and the asterisk command are all considered
this way, characters sent to the 8840A are never lost
c/ue
to
to
be
device-clear commands because the results are so buffer overflow.
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3-14
1
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