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Theory of Operation
3–52
1780R-Series Service Manual
line allows execution of the instruction set to continue. By inserting one
WFS per instruction set, the VRO START signal will control the refresh rate
of the readout.
V UNBLANK (P4.4) controls the blanking of the Z-Axis for the vectorscope
CRT. This signal control line is one of four signals applied to the 4-input
NAND gate, U289A, on the Z-Axis Diagram 35. The NAND gate controls
whether the vectorscope trace is displayed or blanked. Other signals fed to
the NAND gate include /VECT READOUT EN and PHASE BLANK from
the Readout Engine (Diagram 20) and /VECTOR BLNK (Vector Center Dot
Blanking) from Diagram 27.
V UNBLANK enables the vectorscope trace when vector line select mode is
enabled. When in line select mode, V UNBLANK is set low to blank the
vectorscope trace. When set high, the selected lines are displayed.
When the vectorscope is not in line select mode, V UNBLANK is set high
and the vectorscope trace display is controlled by other signals in the
instrument.
V FOCUS (P4.5) and W FOCUS (P5.2) control the focus to the vectorscope
CRT and waveform CRT, respectively. These signals are active low for the
line select mode during 1-, 2-, or 3-line sweeps, but are not activated during
15-line or field rate sweeps. During field rate sweeps and when not in the
line select mode, these lines are set high.
V SKIP WRO (P4.6) is used to skip the waveform CRT readout instruction
set and execute the vectorscope instruction list. This control line is used in
field sweep modes to allow the vectorscope display to be refreshed at a
60 Hz rate while the waveform display is updated at a 30 Hz rate.
WLS LINE (P5.0) controls the blanking of the Z-Axis for the waveform
display. This signal control line is one of four signals applied to a 4-input
NAND gate, U289B, on the Z-Axis Diagram 35. The NAND gate controls
whether the waveform trace is displayed or blanked. The other three signals
fed to the NAND gate are: /WFM READOUT EN and WFM BLANK EN
from the Readout Engine; /RY SCH BLNK from pin 19 of U226 on
Diagram 42.
WLS FIELD (P5.1) controls the intensification of the selected lines in line
select mode when the field sweep mode is selected for the waveform display.
This control signal line is set low for the selected lines in field rate sweeps.
When not in line select mode or not during field rate sweeps, WLS FIELD
goes to the high state.
WRO START (P5.3) is used to start the Readout Engine. If a Wait For Start
(WFS) is used in the readout instruction list, this signal control line allows
execution of the readout instruction list to continue. Normally this control
line is held high and then pulsed low to signal the Readout Engine.