In NTSC systems, the master clock crystal is rated as 53.6931MHz. This is divided by 15 to give 3579540Hz, used as the system clock (for the CPU, PSG and other devices) and also for the RF encoder as the Chrominance subcarrier frequency. Because this latter value is officially set to 315/88 MHz, the clock value of 3579545Hz is commonly used although the difference is negligible.

PAL systems have a master clock crystal rated as 53.2034MHz, which is again divided by 15 to give 3546893Hz as the system clock. The PAL RF chrominance subcarrier frequency of 4.43361875MHz (precisely) is obtained by dividing it by 12. Applying the same reverse logic as before yields a "true" system clock of 3546895Hz, again a negligible difference.




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