Motorola Flash Innovation 2003 – Design Contest
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.