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Register differences vs the original

Added by foft over 4 years ago

Discussion on register differences from the original hardware.

So far I'm considering the following:
D400 (w):
bit 6 added, used together with bit 5
00 = playfield dma off
01 = playfield dma on - original colour clock
10 = playfield dma on - 2x colour clock
11 = playfield dma on - 4x colour clock

D408 (r): HCOUNT

xxl was suggesting making the turbo setting available in the 6502 map. Additionally with a mode that is turbo in vbi only. Which would be faster while still very compatible. I'm not sure where to place that.


Replies (8)

RE: Register differences vs the original - Added by xxl over 4 years ago

This should be a R/W reg.

while read always works, write maybe like this:
sta reg; enable to write here for the next 4 CPU cycles (current)
sta reg; store to turbo reg.

b7 = 0 turbo ON only in vertical blank
b210
111 = off
110 = x2
101 = x4
100 = x8
011 = x16
010 = x32

RE: Register differences vs the original - Added by foft over 4 years ago

I see, to protect against existing writes - which are most likely not repeated. Any thoughts on address?

I'm working on 32x mode... Well I started then went away for Easter:)

RE: Register differences vs the original - Added by xxl over 4 years ago

I dont know. D408 (or D418) looks fine...

RE: Register differences vs the original - Added by foft about 4 years ago

I propose using the same bit of Sophia for hi-res mode colour too:

bit4 PMCTL controls additional color in hi-res mode.

0 - 1 color, 2 luminances (default)
1 - 2 colors

RE: Register differences vs the original - Added by 917k about 4 years ago

That sounds cool to me!

RE: Register differences vs the original - Added by ijor about 4 years ago

Whatever you do, please provide a hardware override to disable any difference.

Any modification or enhancement is a possible source of incompatibility, doesn't matter how remote it could be. Ideal emulation (or clone) IMHO, should be that there is no way to distinguish between the core and original hardware, even if you or me would try on purpose.

So some kind of user configuration should be able to disable turbo, extra video features, etc.

RE: Register differences vs the original - Added by Stephen about 2 years ago

Have any decisions been made here?

I am back up and running, all updated to core 31. I am VERY interested in the ANTIC 2X and 4X modes.

Has the 2 colour hi-res Sophia mode been implemented? If so, how is that activated?

RE: Register differences vs the original - Added by foft almost 2 years ago

Yeah Sophia 2 colour mode and the 2x and 4x are implemented. pm me on atariage if you want to know how to use them. Sorry I don't read this forum like ever pretty much, since no-one posted!!

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