Programming—DM 5010
•
Floating point
numbers expressed in scientific nota
tion.
Examples:
+ 1.0E—2, 1.0E—2, 1.E-2, 0.01 E+0
The
largest acceptable number for an argument is
±3.4028E+38.
Message
Protocol
As the
instrument receives a message it is stored in the
Input
Buffer, processed, and executed. Processing a mes
sage consists of decoding commands, detecting delimiters,
and
checking
syntax. For
setting commands,
the instrument
then
stores the indicated changes
in the
Pending Settings
Buffer.
If
an
error is detected during processing, the instru
ment asserts
SRQ, ignores the remainder of the message,
and
resets
the
Pending Settings Buffer. Resetting the Pend
ing Settings Buffer avoids undesirable states
that could oc
cur
if some
setting commands
are
executed while others in
the same
message are not.
Executing a message consists of performing the actions
specified
by its
command(s).
For
setting
commands,
this
in
volves
updating the instrument
settings
and recording these
updates
in
the Current
Settings Buffer. The
setting com
mands
are
executed
in groups—that is, a series of
setting
commands
is
processed and recorded in the Pending
Settings
Buffer
before execution takes place. This allows
the
user to specify a new
instrument
state without having to
consider
whether
a particular sequence would be valid. Ex
ecution of the
settings occurs when the instrument pro
cesses
the message
terminator,
a
query-output
command,
or
an
operational
command
in a message.
When the
instrument processes
a
query-output
com
mand
in
a message, it executes any preceding
setting
com
mands
to
update
the
state of the instrument. It then
executes
the
query-output
command
by
retrieving the ap
propriate data and
putting it
in the Output Buffer. Then, pro
cessing
and
execution continue for the remainder of the
message.
The data are sent to the controller when the in
strument is
made a
talker.
When
the instrument processes
an
operational
command
in a message, it executes any preceding
setting commands
before
executing the
operational
command.
Multiple
Messages
The
Input Buffer has
finite
capacity
and a single message
may be long enough to
fill it.
In this case, a portion of the
message
is processed before the instrument
accepts
addi
tional
input. During command processing the instrument
holds off
additional data (by asserting NRFD) until space is
available
in the buffer.
When
space is available, the
instrument can accept a
second
message before the
first has been processed. How
ever,
it holds off additional messages with NRFD until it
completes
processing the first.
After the instrument executes a
query-output
command
in a message, it holds the response in its Output Buffer until
the
controller makes the instrument a
talker. If the instru
ment receives
a
new
message before all of the output from
the
previous
message is read, it clears the Output Buffer
before
executing the
new message. This prevents the con
troller from getting unwanted data from old messages.
One other situation
may
cause the
instrument to delete
output. The execution of a long
message might cause both
the Input and
Output buffers to
become full. When
this oc
curs,
the
instrument cannot finish executing the message
because
it
is waiting for
the
controller to read the data it has
generated;
but the
controller cannot read the data because
it
is waiting
to finish sending its message. Because the
in
strument
’s
Input buffer is
full and it is holding off the rest
of
the controllers
message with NRFD, the system is hung
up
with
the controller and
instrument waiting for each other.
When the
instrument detects this condition, it
generates an
error, assets SRQ, and
deletes the data in the Output
buff
er.
This
action allows the controller to transmit the rest of
the message and informs
the controller that the message
was
executed
and
that the output was deleted.
A
TM
5000
instrument can be made a talker without hav
ing received
a message that specifies what it should output.
In this case,
acquisition instruments (counters and multi
meters) return
a measurement if one is ready. If no mea
surement is ready,
they return a single byte
message with all
bits equal to
1 (with message terminator); other TM 5000
instruments
will
return
only this message.
Instrument
Response to IEEE-488 Interlace
Messages
Interface messages and their effects on the instrument’s
interface
functions
are defined
in IEEE Standard 488-1978.
Abbreviations
from the
standard are used
in this discussion,
which
describes the
effects of
interface messages on instru
ment operation.
UNL—
Unlisten
(63 with
ATN)
UNT—
Untalk (95 with
ATN)
When
the UNL command
is received, the instrument’s
listener function goes to its idle state (unaddressed).
In the
idle
state,
the instrument will
not accept instrument com
mands
from the GPIB.
3-22
Summary of Contents for DM 5010
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