NTSC Video Signal Produced by Motorola 68HC908QY4

The project utilizes the Motorola 68HC908QY4 in order to produce an NTSC video signal which is applicable in various purposes.

An interrupt timer is included in the Motorola 68HC908QY4 which is used to generate an interrupt every 455 bus cycles. This results to the frequency of NTSC sync which is the same as the interrupt rate of 15.734kHz. It uses a 28.6363MHz clock to make the bus speed of the QY4 at 7.15909MHz which is twice the chroma frequency of 3.579545MHz.

The main line consists of a table of NOPs because the interrupts that occur in the middle of a multicycle instruction are not recognized unless the instruction is completed. During the interrupt, all of the sync functions are performed. This returns the interrupt routine to the start of the NOP table. There are several applications that employ QY4 to produce NTSC sync and they include interlace quality, high-voltage regulation, and an NTSC test-pattern generator that produces simple test patterns for evaluating the geometric distortion of a TV. Another application is a VCR pacifier, that includes RTC, where an audio-only signal such as from a radio is recorded by a VCR.