M2 and MMC3

Discuss emulation of the Nintendo Entertainment System and Famicom.

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Anes
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M2 and MMC3

Post by Anes »

The Wiki says:
The MMC3 scanline counter is based entirely on PPU A12, triggered on rising edges (after the line remains low for two rising edges of M2).
Can somebody explain me what is "M2"?
Thxs
ANes
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Zepper
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Re: M2 and MMC3

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lidnariq
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Re: M2 and MMC3

Post by lidnariq »

M2 is specifically the external CPU cycle signal.

It is not the master clock.
It is not the APU or DMA clocks.
It is not the PPU pixel or colorburst clock.

In the 2A03, it is high for 5/8 of the time and low for 3/8. The exact phase of it relative to the PPU is random, so the exact rise/fall time of M2 matters relative to PPU events.
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Anes
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Location: Mendoza, Argentina

Re: M2 and MMC3

Post by Anes »

Thxs a lot to both!!
ANes
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