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Theory of Operation
- 067-1039-00
setting
FF1 to 1, but the Remainder Counter is not incremented.
During pattern
field
1,
when the
Remainder
Counter
signals
"pattern
too
small"
and
FF1 is
set,
the
Line Spacing Memory is
incremented
each time the signal
is received.
Flip-flop
FF1 is reset
during vertical
blanking
at
the
end
of
pattern
field
1.
The Line Spacing Reset logic
clears
the Line Spacing Memory when
the
pattern
is
too
big.
The pattern
is too big when the start
of
vertical
blanking
occurs before
the last
white line
is
generated
in
both
fields.
This condition
occurs when the number of LINES PER TWO
FIELDS swith is decreased
by more than- [2(Remainder)].
Flip-flop
FF2 remembers if the pattern
in field
zero was too big.
If V Blanking starts
before
the last
white line
is
generated
in
field
1 and
FF2 is
se~,
the Line Spacing Memory is cleared.
The
correct
spacing is then set by the Line Spacing Increment
circuit.
Flip-flop
FF2 is cleared
whenever
all
white
lines
have
been
output
(A= 1).
Line Spacing Memory
The Line
Spacing
Memory is
an
eight-bit
binary
up-counter
consisting
of
U555 and
U545.
It contains
the number of dark scan
lines
between white lines.
For example, if the
memory contains
the
number 10 and scan line
number (i
+
1) is a white line,
then scan line
number (i
+
11) is also a white line.
Soan Line Counter and White Line Generator
This circuit
consists
of an eight-bit
binary up-counter
(U775 and
U565),
an
eight-bit
comparator
(U655), a set-reset
flip-flop
(U675B
and U675C, and another
eight-bit
comparator
(White
Line
Generator
U665).
The Scan Line Counter is reset
to zero during
vertical
blanking
or after
the last
white line of the current
field
has been generated.
When not reset,
the Scan Line Counter counts up
from
zero
each
horizontal
scan
line until
the counter value equals
the Line Spacing
Memory. These two values
are compared by U655.
The output pin 13 of
this
comparator goes to a high state
when the counter
equals the Line
Spacing Memory and sets
the set-reset
flip-flop
U675B and U675C.
The
3-10
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