Trigger Source Display Messages - Keithley 194 Instruction Manual

OPERATION
3.6.1 Trigger Source
The trigger source is selected by pressing the SOURCE key.
The instrument will display one of the trigger sources, as
summarized in Table 3-3. To select a different source, press
uprange or downrange repeatedly until the desired trig-
ger source is displayed. The new trigger source is saved
once the source is displayed. To return to the previous
mode, press SOURCE.
Note that the SOURCE key is inoperative when the instru-
ment is in the dual-channel display mode.
NOTE
When you select external, input signal, or other
channel triggering, you must first arm the AID
converter by pressing the TRIGGER button. The
measurement sequence will then begin when the
appropriate trigger stimulus occurs.
Table 3-3. Trigger Source Display Messages
Message
Selected Trigger Source
LMMEDIATE
TRlGGER button or IEEE trig-
gcr (X, GET, etc.)
EXTERNAL
Pulse applied to TRIGGER IN
jack.
INPUT SIGNAL Input signal, depending on
selected slope and levels.
OTHER CHANNEL Second channel when 1944 op-
tion installed.
TRIG ON TALK
IEEE talk command
TRIG ON X IEEE X command
TRIG ON GET IEEE GET command
3.62 Single/Continuous Arming Modes
A/D arming can be set up to operate in two different ways:
in continuous or single modes. In a continuous mode, the
unit will automatically rearm the A/D converter after each
measurement sequence. The unit will then perform
another measurement sequence when it receives the ap-
propriate trigger stimulus (as selected with the SOURCE
key). In the single mode, however, the A/D converter must
be manually re-armed after each measurement (the A/D
converter can be re-armed from the front panel by press-
ing TRIGGER).
Single/continuous arming selection is performed by press-
ing the SGLiCONT button to select the desired mode; the
appropriate indicator will then display the selected mode.
3-10
When the instrument is in the dual-channel display mode,
the SGLiCONT button and associated indicators are
inoperative.
NOTES:
I. If the instrument is in the immediate (TRIGGER button),
continuous mode, it will process measurements con-
tinuously without requiring additional triggers.
2. If the selected trigger source is the input signal, exter-
nal trigger, or other channel, the unit will require a
separate trigger stimulus for each measurement
regardless of whether the unit is in the single or con-
tinuous armed modes.
3. When going from the single, immediate mode to the
continuous, immediate mode, it will be necessary fol
you to press the TRIGGER button to begin processing
measurements.
4. The decimal point in the display (between second and
third digits from the right) will turn on to indicate that
the A/D converter is armed and waiting for a trigger.
Discussion
Basically, there are two steps needed for initiating a
measurement sequence. First, the A/D converter must be
armed, so that it is running and processing data. Second-
ly, the unit must be triggered by the appropriate trigger
stimulus (determined by the selected source) before it will
perform a measurement sequence. The only exception to
this two-step process is when the immediate, front panel
mode is selected. In this situation, pressing TRIGGER per-
forms both steps simultaneously so that the A/D converter
is armed and the measurement is initiated with a single
action.
There are two fundamental reasons why the A/D converter
must be running before a measurement sequence takes
place. First, when input signal triggering is in effect, the
A/D converter must supply input signal amplitude data
to the digital comparator circuits so that they can trigger
a measurement when the programmed trigger threshold
is reached. Secondly, when using pre- or post-trigger, the
unit must continuously store data so that it can later flag
the beginning of the measurement relative to the pro-
grammed trigger point.
3.6.3 TRIGGER Button Operation
The Model 194 can be triggered by the front panel TRIG-
GER button, if the immediate mode has been selected as
the trigger source (paragraph 3.6.1). Once activated, press-
ing TRIGGER will initiate a single or continuous sequence
of measurements, depending which of those two modes
was selected with the SGLiCONT button.