Atari STEEPLECHASE, Руководство по эксплуатации, техническому обслуживанию и ремонту

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register device in location Cl insures that no pickets are
present when a new play mode begins. Then an additional
"1" is circulated in the register as each new picket appears,
until all six bits are ones, meaning that all pickets are on
the screen.
3.4.7 HORSE HORIZONTAL MOTION COUNTERS
(SHEET 2 ZONES A, B, C, D 4 AND 5): A
total of seven
horse motion counters are provided, one for the pace horse
and one for each of the player horses. For example, the
type-9316 devices in locations N2 and P2 form the counter
for player horse #1. The counters are driven by the
HCLOCK
1 through
HCLOCK
4 signals derived from the main system
clock (see para. 3.4.2}. Each horizontal motion counter
can be programmed to divide by either 256 or 255 or 254.
If a motion counter counts 255 pulses, the horse image on
the TV screen does not move along the racetrack because
the
HCLOCK
1 through
HCLOCK
4 signals have exactly
255 pulses per horizontal scan line on the TV screen.
av
Now consider a specific motion counter for one of the
player horses, say horse #1. If the
REV
1 signal, applied at
K2 pin 6 and N2 pin 4, is high, then the motion counter
will divide by 254. This will cause horse #1 to move to the
left (drop back) on the screen. But if
REV
1 is low and the
FWD 1 signal, applied at K2 pin 5, is high, then the motion
counter divides by 256. This will cause the horse to move
to the right (advance towards the finish line}. The other
motion counters operate in a similar fashion. Note: The
Atari motion circuit is protected by U.S. patent no.
3,793,483.
The
REV
signals are generated by the Jump and Fall
Circuitry (see para. 3.4.9). An individual
REV
signal (
REV
1,
REV
2, etc.) is high only on one or two horizontal scan
lines per frame on the TV screen, depending on the fre­
quency of the
TRACK CLOCK
signal, and only when the
horse is falling.
16V
J7JlJLJ7J1SlS1_JLJ7_
32V
64V
l
L
128V
\
L
256V
7J
u-
VBLANK
_J
I
VSYNC
n
fL
VF1
LJ
u-
TRACK
Figure 3-3 Timing Diagram of Signals Associated with Vertical Picture Frame
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