|
NTSC
Video Using the 68HC908QY4
The Motorola 68HC908QY4 is used
to produce an NTSC video signal that can be used in several
applications. By using a 28.63636-MHz clock, the ‘908QY4 bus
speed is 7.15909 MHz, which is twice the chroma frequency
of 3.579545 MHz. The interrupt timer is used to generate an
interrupt every 455 bus cycles, resulting in an interrupt
rate of 15.734 kHz, which is the frequency of NTSC sync. Because
interrupts that occur in the middle of a multicycle instruction
are not recognized until the instruction is completed, the
main line consists of a table of NOPs. All of the sync functions
are performed during the interrupt, and the interrupt routine
is returned to the start of the NOP table. The ‘908QY4 can
be used to produce NTSC sync for applications such as an NTSC
test-pattern generator that produces simple test patterns
in order to evaluate a TV’s geometric distortion, high-voltage
regulation, and interlace quality.
Jed Margolin
U.S.
jm@jmargolin.com
|
|
