Clock

Not to be confused with the real time clock (RTC), which is clocked independently.

File:Clkdistribution.png

In cartridge systems

The main system clock (often called mclk) is either 24MHz (MVS) or 24.167829MHz (AES). It is generated and divided by 2, 4 and 8 by NEO-D0 from a crystal oscillator, to provide the 12MHz clock for NEO-ZMC2, the inverted 6MHz one for video output and also the 3MHz one for NEO-B1.

LSPC2-A2 divides it by 3 and 6 to provide the 8MHz clock for the YM2610 and the 4MHz one for the Z80.

The cartridge connector provides the 24MHz, 12MHz, 8MHz and 4MHz inverted clock signals.

A second quartz oscillator is used for generating the color burst needed by composite video, for the video encoders.

A third 32768Hz quartz oscillator is used for the RTC.

Phase relations

Signals

24M, 12M, 68KCLK, 68KCLKB, 8M, 6MB, 4M, 4MB, 1MB

In CD systems

File:Cd2 quartz.jpg

System clock and video PLL circuit on a CDM3-2 board.

NEO-GRC ?