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External Gate Mode; Internal Gate Mode; Rate Generator Output In External Gate Mode - HP 8081A Operating And Service Manual

300mhz rate generator module
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3-31
Vary the EXT INPUT LEVEL switch
®
and
note that the trigger output disappears when the thre-
shold level reaches approximately +0.2V. Set the exter-
nal input level to -1 V.
3-32
Set the NEG-POS-MAN switch @to NEG.
Set the pulse generator output polarity to negative.
This gate signa I can come from either an external source
(
via the EXT INPUT connector
(J)
or locally using the
MAN pushbutton
®.
When the gate signal switches on,
the first output pulse is always started at the beginning.
When the gate signal switches off, the pulse is terminated
immediately, i. e. the last pulse may be cut short.
3-37
In External Gate mode the repetition rate
generator output is enabled/disabled by a gate signal.
3-33
The oscilloscope display should be similar to
that shown in figure 3-4 except that the external input
is a negative-going pulse.
3-34
Vary the EXT INPUT LEVEL switch
®
and
note that the trigger output disappears when the thre-
shold level reaches approximately -O.2V.
3-35
As mentioned previously, the pulse output
in trigger mode can also be produced using the MAN
pushbutton
®.
First set the NEG-POS-MAN switch
®
to MAN. This transfers the trigger input from the EXT
INPUT connector
(J)
to the MAN pushbutton
@ .
Set
the oscilloscope timebase to about 0.2 sec/em and trig-
ger internally. Press the MAN pushbutton
@
and note
that the pulse output goes high when the button is pres-
sed and low when it is released. The EXT INPUT
LEVEL control
®
has no effect in this mode.
Internal Gate Mode
3-39
Set the NEG-POS-MAN switch
@
to POS
and the EXT INPUT LEVE L control
®
to -1 V. Vary
the rate VERNIER
C2>.
Note that the last pulse may be
cut short by the gate turning off (see figure 3-5).
3-38
Set the Mode switch
®
to EXT GATE. Set
the oscilloscope timebase to 2 usee/em and trigger inter-
nally. Press the MAN pushbutton and note that the rep.
rate generator runs at the selected rate for as long as the
button is held down.
3-41
Internal Gate mode can only be used if an
8084A 300 MHz Word Generator module is available. In
this mode of operation the gate pulse for the rate genera-
tor comes from the word generator via an internal con-
nection. This gate enables the rate generator output in
the same way as an external gate. The purpose of this
mode is to enable an exact number of data bits to be
gated out of the word generator.
3-40
External Gate Mode.
3-36
EXTERNAL
OV
INPUT
Gate on
Gate off
RATE
GENERATOR
O v - - - - - - - ;
OUTPUT
Last pulse may not be completed
Figure 3-5. Rate Generator Output in External Gate Mode.

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