6
When RUN/HOLD is set to HOLD, the remaining 3K words per
channel of the digitising memory are set to zeroes and the
disabled functions are restored. Pre-trigger time delay is limited
to 10 divisions in FAST mode.
In "roll" and "repeat" modes the RATE key is disabled.
R14. ROLL MODE OPERATION
In "roll" mode new data is written onto the right-hand side of the
display as digitising takes place. Thus the waveform appears to
roll across the screen. The operation of the DSA524 in "roll"
mode (timebase speeds of 200msecs and below) is different from
its operation in other modes in several respects:
a) Triggering and Display Update Rate
Because the waveform data is written continuously onto the dis-
play, it is not necessary to continually stop and restart the digiti-
sing process. Consequently when RUN /HOLD is set to RUN,
digitising takes place continuously and triggering is disabled. The
RATE key is disabled.
When RUN/HOLD is set to HOLD, triggering is enabled for
operation via the SINGLE key. Pressing SINGLE commences the
"roll" and the trigger event stops it, thus the waveform data
captured is entirely pre-trigger data. Consequently if a trigger
occurs immediately, no data will be captured unless some post-
trigger time delay has been set. When the trigger mode is set to
AUTO, triggering occurs immediately. When the trigger mode is
set to NORM, triggering occurs synchronously with the trigger
signal.
Because in "roll" mode the trigger stops the digitising process
instead of starting it, all the data in the digitising memory is pre-
trigger data unless some post-trigger time delay has been set.
Pre-trigger time delay is therefore not needed and is disabled.
b) Display Window and Search mode
Because the waveform data is written continuously to the screen
as digitising takes place, the display shows the last part of the 4K
digitising memory instead of the first part. Because the left hand
edge of the display window is set in steps of 100 words, only 996
words are displayed and the remaining 28 words are set to zero.
SEARCH can only be selected in HOLD, and the scan window is
initially set fully to the right instead of fully to the left.
c) Trace Controls
When in roll mode, operation of any of the trace controls (e.g.
gain variable) will effect only the waveform data on the display
which was captured after the control was changed. However,
when the digitising process is stopped, the new trace control
values will be applied to the whole of the contents of the
digitising memory including waveform data captured before the
change was made.
R15. REPEAT MODE OPERATION
In normal mode the DSA524 can digitise a waveform at up to
20MS /s digitising rate, equivalent to 5usecs per division. If the
waveform is repetitive (as opposed to being a single event) it can
digitise the waveform repetitively, gradually building up the data
in the digitising memory. This mode of operation, known as
"repeat" mode, is used for timebase speeds of 2usecs and above
and provides equivalent digitising rates of up to 2GS /s (50nsecs
per div.). The operation of the DSA524 in repeat mode is
different from its operation in normal mode in several respects:
a) Triggering
Repeat mode requires a synchronously triggered waveform,
AUTO and LINE trigger modes are therefore disabled. Time delay
is not available (neither pre nor post trigger). The trigger event is
not captured, the first section of the waveform captured starts
350 nanoseconds after the trigger event.
b) Display Update Rate
Repeat mode involves complex manipulation of data which can
take several seconds per digitisation. The display update rate
varies between about one per second for a single channel at
2usecs/div to one every 10 seconds for both channels at
50nsecs/div. The Rate key is disabled in repeat mode.
R16. CURSOR MEASUREMENT
Moveable cursors allow accurate measurements of voltage and
time to be made on either Trace A or Trace B via an on-screen
digital readout.
To select cursor measurement, press the key marked ON/OFF
within the numeric keypad. Cursors will appear on Trace A, and
Trace B will be suppressed. Pressing the key marked A/ B
selects Trace B instead of Trace A. To turn cursor measurement
off press the ON/OFF key again.
Cursor measurement.
The cursors are flashing horizontal lines which each terminate
at a point on the waveform. The reference cursor is on the left
hand side of the screen, the delta cursor is on the right hand
side. The measurement is made between the two lines. The
readout shows the voltage and time difference between the end
of the reference cursor line and the start of the delta cursor
line. The cursors are moved using the arrow keys marked REF
CURS and ∆ CURS respectively.
R17. PROGRAM MODE
The DSA524 can operate as a fully programmable instrument. It
can "learn" individual or sequential front panel settings, store
them in non-volatile memory, and "replay" them on demand.
Up to 50 settings can be stored.
Each front panel setting includes the state of every key and
rotary control and the source of each trace waveform. Thus if a
setting is "learned" which includes a trace recalled from a wave-
form store, that same store will be recalled again when the set-
ting is "re-played". Thus reference waveforms can be recalled
automatically within PROGRAM mode.
To "learn" one or more settings press the LEARN key, this turns
on learn mode. The display will show the message "NEXT
POSITION = NN" for 3 seconds where NN is a number between
01 and 50 corresponding to the position set when the unit was
last used.
To store a front panel setting in this position, ensure that the
front panel is set as required and press the SET/NEXT key. The
display will show the message "STORED IN NN" followed by
"NEXT POSITION = NN + 1". To store another front panel set-
ting, reset the front panel as required and press the SET/NEXT
key again. To store the setting in any other memory position,
press the SET(NN) key followed by a two digit number between
01 and 50.
The next memory position can be checked at any time by
pressing the LEARN key again.
To "replay" one or more settings press the REPLAY key, this
turns on replay mode. The display will show "NEXT POSITION =
NN" as for learn mode. To replay the front panel setting cor-
responding to this position press the SET/NEXT key. The display
will show "REPLAYED FROM NN" followed by "NEXT POSITION
= NN + 1". Press the SET/NEXT key again to replay this next
position. To replay any other position press the SETINN) key
followed by a two digit number between 01 and 50.
The next memory position can be checked at any time by
pressing the REPLAY key again.
Whenever the front panel is set using the replay mode all the
rotary controls become inoperative. To make any rotary control
operative again press the key directly to its right. (Press once if
the lamp above the key is on, or twice if it is off.)
To exit either learn or replay modes press the LEARN and
REPLAY keys simultaneously.