Re: [stella] TIA latch timing

Subject: Re: [stella] TIA latch timing
From: "Glenn Saunders" <cybpunks@xxxxxxxxxxx>
Date: Tue, 16 Oct 2001 11:29:43 -0700
Is there a list somewhere which indicates the number of cycles after WSYNC
when each TIA register is latched?  e.g. I believe the playfield registers
are latched on color cycles 68 and 148 (left edge and middle of screen), so
any updates to those registers need to be completed by CPU cycle 22 and 49.

In my experience playing around with playfield rewrites, the playfield registers can be rewritten at any time and they will respond appropriately. Not that you'd want to in most cases, but it can be done. In other words, you could update PF2 after half of its previous contents are being rendered to the screen. This would be more practical with the color registers, so you can have half of PF2 with one color and half with the other.

It appears to me as if the TIA registers latch immediately, meaning anything you write to them will persist no matter when you write to them on subsequent scanlines, if that's what you mean by latch.

A more important table would be the start and end times for when the playfield and sprite registers are scanned to the screen in order to aid programmers in avoiding unintentionally stomping on the data during dynamic register rewrites.

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