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


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 Chipicon.png NEO-D0 from a crystal oscillator, to provide the 12MHz clock for Chipicon.png NEO-ZMC2, the inverted 6MHz one for video output and also the 3MHz one for Chipicon.png NEO-B1.

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

To do: 8M is 33high/66low, not 50/50



Sig.png24M (~24MHz), Sig.png12M (12MHz), Sig.png68KCLK (12MHz), Sig.png68KCLKB (12MHz), Sig.png8M (8MHz), Sig.png6MB (6MHz), Sig.png4M (12MHz), Sig.png4MB (4MHz), Sig.png1MB (3MHz)

In CD systems

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

Chipicon.png NEO-GRC ?