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to go low and HSWP to go high. (Note that HSWP is set high approximately 500 ps after
occurrence of the Instrument Bus SET command. This time delay allows Al5 Controller to
perform certain functions before the sweep starts.)
To clear HSWP, Instrument Bus 13 is set high, Address 50 is selected, and (when the
IF-Display Section address strobe occurs) U12A, U12B, U4A, and U4B are cleared. HSWP
may also be cleared by other assemblies in the A3 Digital Storage when the RSHS line goes
low.
In Fast Sweep mode (sweep time setting 210 ms), HSWP is no longer used to control the RF
Section sweep ramp, since the spectrum analyzer is not sweeping the RF Section frequency. It
is normal to see the green front-panel sweep LED turn off for these settings, even though the
CRT trace is sweeping.
Free Run Mode (for Sweep Time 220 ms)
When the RF Section is in Free Run mode with sweep time settings 220 ms, the sweep is
started when the Instrument Bus sets HSWP. The sweep is stopped by the RSHS line from
controls the time from the end of one sweep to the beginning of the next sweep (sweep dead
time).
Line, Video, and External Triggers (for Sweep Time 220 ms).
The RF Section can direct A3Al to set HSWP high when a line, video, or external trigger
occurs. If Instrument Bus line 14 is high and U18 is strobed with Address 50, U18 pin 13 will
go low, setting U4A pin 9 high, which triggers U94. At the end of the pulse generated by
output (pin 6) of trigger multiplexer U16 in the Trigger generator will then cause U12A to
be clocked on a negative-going transition of the selected trigger input. Refer to "Fast Sweep
Generator" in this chapter.
Recorder Pen Lift Driver
In sweep time settings 220 ms, the Recorder Pen Lift Driver supplies the PENLIFT signal to
the rear-panel PENLIFT connector. PENLIFT may also be used to control blanking of an
external CRT display.
is in progress (HSWP is high, PENLIFT is 0 V) and lifts the pen when a sweep is not in
progress (HSWP is low, PENLIFT is 15 V). Decoder U3A is a noninverting buffer that drives
Q15 from the HSWP line.
Sweep Trigger @
The Sweep Trigger circuit produces triggers for all sweep times. It contains the video,
external, and line trigger circuits, the fast sweep Free Run Oscillator, the trigger multiplexer,
and the fast-sweep Auto Trigger circuit. A valid trigger for the Fast Sweep Generator or the
High Sweep Control circuit is produced by a negative-going transition at the selected input of
trigger multiplexer U16. This trigger signal will start a sweep only if the Fast Sweep Control
and High Sweep Control circuits are in the proper states.
2 A3Al
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