Tektronix 222 Operator's Manual page 105

More On How It Works-222 DSO Operators
If the Trigger SOURCE waveform is off screen, the trigger point indi-
cator (+ ) is placed at the top or bottom of the display area to show the
direction to the off-screen waveform.
6.9 TRIGGER LEVELIAUTO LVL: PUSH
The Trigger LEVEL control sets the voltage threshold that the signal
must cross to produce triggering. When the trigger signal is dis-
played, the trigger point indicator "
+ "
will be located on that
waveform at the Trigger LEVEL and Trigger POS settings. The trigger
signal need not be positioned within the graticule area to be used as
the Trigger SOURCE. When the oscilloscope is triggered by a signal
that is out of the graticule area, the trigger indicator "
+
"
will be seen
either at the top or bottom of the graticule to show the direction to the
off-screen trigger signal. In AUTO LVL Trigger MODE, the Trigger
LEVEL is set to the midpoint between the peak-to-peak limits of the
trigger signal each time the trigger signal is lost. For other Trigger
MODES, the Trigger LEVEL control may by be set to any level within
the vertical amplifier dynamic range for a particular VOLTSIDIV
setting.
In any Trigger MODE, the AUTO LVL: PUSH button may be pressed to
set the LEVEL setting to the midpoint value of the trigger signal.
6.1 0 ACQUISITIONS MODES
A choice is made by first pressing the button to display the
acquisition mode menu. Further presses of the button cycles through
the choices while the menu is being displayed. The selected mode is
boxed in the menu. Direct selection of the acquisition mode is made
by pressing the menu-select button next to that choice.
NORM: One sample point is acquired and displayed for each sample
interval.
ENV: The positive and negative peak signal values that occur during
a sample interval are acquired and displayed. ENV acquisition mode
is available for SECIDIV settings from 20
JLS
to 20 sec per division.
The sample rate for ENV mode acquisition is 10 MHz.
AVG: The waveform displayed is a moving four-point average of the
last four acquisitions.
REV JUN 1989 6-13