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The horizontal and vertical syncs[1] (along with the system clock) can be inputs on the video connector. That's what enabled all of the 3rd party genlock hardware. It was designed into the Agnus from the start.

Without that you'd need an external framebuffer like an infinite window TBC, which is much more expensive.

[1] ERSY mode: http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_gui...

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Right, 3rd party, not native to the Amiga which the person I replied to was seemingly implying.

No I get what's meant though. The fact that the Amiga apparently had the native ability to sync its PLL to incoming sync signals (and presumably other clocks are derived from that?) is, for the time and for a general purpose micro at least, nothing short of amazing to me.

I disagree for the reason that the hardware that is synchronizing the video is the Amiga itself, not the 3rd party hardware.

https://retrocomputing.stackexchange.com/questions/22320/wha...

The PLL is external, but the chipset had the ability to accept an external clock from the start in the Amiga 1000.

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