VDC secret registers

If you’ve coded for the PCE, especially in assembly and directly accessed the video hardware, you should have noticed that there’s a gap in the register list. Regs $03 and $04 are skipped. A couple of years back, with some discovery by tests Charles Macdonald had done, I eventually figured out that the key to using these registers – is to set the VRAM READ pointer. Depending on the bits set in the WORD buffer of that register, reading from $03 (IIRC, one the regs), enables or disables certain things of the VDC. It has minimal application outside of a few demo effects (mostly distortion type). But recently, it got me thinking. What I never tested… was if I could get the VDC to re-read any of the X/Y/CR/etc regs from the buffer – via these regs. Would be kinda neat for horizontal split screen scrolling and such, if possible. Just a note for when I get my console hardware back up and running.

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