A57 Marker/Bandcross Assembly - HP 8340B Manual
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A57 MARKER/BANDCROSS ASSEMBLY
The A57 marker/bandcross assembly generates the z-axis signal required to place intensity markers
on
an external
CRT.
If
enabled, amplitude markers are generated by sending
a
marker
signal to the
leveling circuits.
The same
circuits that
detect markers are used
to
detect band crossings or the end of
sweep. These
circuits both
cause
the
sweep
to stop and
activate the instrument processor. Other
circuits interface with the rear panel connections. During self test,
hardware on
this
assembly
verifies
that the instrument
processor data
bus
is
operating.
Sweep Event Memory
The sweep-event memory stores numbers that
correspond
to
voltages
on the
0-10V
sweep
signal.
Each number
stored
in
the memory represents
a
single
sweep
event.
Sweep events are detected
by
the
sweep comparator, which compares them
against the
0-10V sweep
ramp.
Sweep
events include:
•
Turning
markers
on and
off
•
Stopping the sweep for
a
bandcrossing
•
Stopping the sweep for the end-of-sweep
and retrace
The sweep comparator also
finds the current
sweep position when you make changes
in
frequency
parameters
during an analog
sweep
longer
than
300
ms.
Manual Sweep
DAC
The
manual
sweep DAC generates
the
sweep-out
signal
when the instrument
is in
CW
or manual
mode.
Sweep
Control Block
The sweep
control block allows the
sweep
to be
stopped either from the rear
panel, or by the
sweep
comparator. With the
CRT Z-axis
control circuits, the sweep can be blanked on
a
display for band-
crossing or retrace, and markers can
be intensified.
Low Bandcross (LBX)
The A57 marker/bandcross assembly uses
the LBX (low bandcross) signal to stop the analog
sweep
at positions previously loaded
in
the sweep event memory by the instrument processor. When LBX
is
low, the
A59 digital
interface
causes the
instrument processor to run, allowing the instrument
pro¬
cessor to perform the tasks necessary for the
sweep
to proceed. This happens either at
a
bandcross¬
ing,
or at retrace at the end of
a
sweep.
HP 8340B/41B
Controller Section Theory of Operation
F-3
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