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the A3 Digital Storage section and in the spectrum analyzer RF section. Instrument Bus
commands set the HSWP line high or low, or program HSWP to go high when a sweep trigger
occurs. Trigger sources that may be selected are: the line, the video signal, or an external
trigger input from the instrument rear panel. A3Al Trigger contains circuits that select and
process trigger signals. It also contains the Fast Sweep Generator, which produces a linear
ramp voltage (0 V to approximately +2.2 V) used as a horizontal sweep for the CRT display.
This sweep ramp is used only with FREQUENCY SPAN=0 Hz. (It is not used to sweep the
RF Section frequency.)
The fast sweep ramp is applied to AlA X Deflection Amplifier or AlA XYZ Driver
Amplifier when selected by an analog multiplexer in A3A2 Intensity Control. The fast sweep
time may be varied in a 1, 2, 5 sequence from 10 ms (1 ms/div) to 1~s (100 ns/div). Trigger
circuitry used for the triggering of RF Section sweeps (by HSWP) is used to trigger fast
sweeps.
Control.
High Sweep Control @
The High Sweep Control circuit generates HSWP, which is a TTL open-collector signal that
is used by A3 Digital Storage to control signal tracking and conversion. HSWP is also used
in the instrument RF Section to control the Sweep Generator circuitry. The sweep ramp is in
progress when HWSP is high and is stopped (at any point during the sweep) when HSWP is
low. The RF Section can also pull HSWP low to stop the sweep under certain conditions. For
example, when a front-panel key is pressed, the main processor in the RF Section pulls HSWP
low (on Al2 Front Panel Interface) to immediately stop the sweep, then programs HSWP low
(on A3Al Trigger) with an Instrument Bus command before servicing the front-panel request.
HSWP must be set high again (on A3Al Trigger) for the sweep in the RF Section to resume.
HSWP is used directly to light the green front-panel SWEEP LED on the IF-Display Section.
This LED provides a very quick method of checking for activity on the HSWP line.
HSWP Generation
For HSWP to be high, flip-flop U12A pin 6 must be low. Inverter U7A buffers U12A
and provides the open collector drive for the HSWP line. U12A is set and cleared by the
Instrument Bus and can be cleared by the RSHS signal from A3A6 Main Control. To set
HSWP, Instrument Bus bits 14 and 15 are set high, Address 50 is selected, and address
decoder U18 is enabled by LTIO (the IF-Display Section address strobe). U18, pin 13 goes
low, which clocks the U4A and U4B Q outputs high. The positive-going transition at the
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