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Theory of Operation
1780R-Series Service Manual
3–51
are ANDed together in U167 to produce a frame sync pulse. The frame sync
pulse interrupts the Line Rate Controller and causes the line counter to be
reset to zero, and resets the Static RAM stack pointer. In the 1781R 2 of 8
mode the BRUCH frame pulse provides the interrupt through U167. This is
a negative edge signal that occurs on line 7 of field 1 and field 5. In the 1 of
4 and 1 of 8 modes, the FIELD 1 pulse is also a negative edge signal that
occurs on line 7 of field 1 in PAL or line 11 of field 1 in NTSC.
The BRUCH Frame Pulse and FIELD 1 signals are enabled by P1.1 and
P1.0 as part of the start TaskData that is sent to the Line Rate Controller over
the Internal Data Bus. ID0-ID7, /RD, /WR, /LRC, and IA0 communicate
bi-directionally with the Master MPU.
Output Signals. The following control signals are generated by the Line Rate
Controller (Processor U367):
FIELD 1 ENABLE (P1.0), when set to high, enables the field 1 pulse for
triggering (interrupting) the Line Rate Controller. For NTSC this occurs on
line 7 of field 1 every four fields. For PAL this occurs on line 316 (third line
of field 2) every eight fields.
BRUCH PUL ENABLE (P1.1), when set high, enables the BRUCH Pulse
for triggering (interrupting) the Line Rate Controller. This triggering mode is
only used for PAL and occurs on line 316 every four fields.
RO RESET (P1.6) resets the Readout Engine on Diagram 20. The Clear line
goes high when RO RESET is active high to cause the Readout Control &
Skip Instruction state machine to go to a known state (State A). RO RESET
is normally executed on power up only.
VRO BURST (P4.0) informs the Readout Engine that the vectorscope is
operating in line select mode. During readout, VRO BURST tells the
Readout Engine to display all readout in the burst mode instead of 2 of 4 line
mode.
VRO ONLY (P4.1) is used when the Vectorscope CRT is used to display
readout only. This control line tells the Readout Engine to display all readout
in the burst mode and not return the display control back to vectors.
VRO INHB (P4.2) is ANDed with WRO INHB (P5.4) to generate the RO
INHB shutdown signal for the Readout Engine. When not in line select
mode, VRO INHB is set to high. In line select mode, this signal line goes
low and disables the Readout Engine one or more lines before the selected
line. VRO INHB is held low until after the last selected line is displayed in
the field. This control line then goes high so that the Readout Engine can
start up.
VRO START (P4.3) is used to start the Readout Engine. If a Wait For Start
(WFS at pin 17 of U385 on Diagram 20) is used, the VRO START signal