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Justin Payne

Member Since 25 Sep 2010
OFFLINE Last Active Apr 15 2019 9:54 PM

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Values applied to SDMCTL. Not quite understanding

Sat Mar 23, 2019 9:56 AM

I'm going through the source for Fort Apocalypse and right off the bat I'm in need of some clarification.


LDA #%00111110

Looking into applying values to SDMCRL, it seems that the value applied doesn't seem to make sense. Mapping the Atari is also throwing me off a bit (rim shot), and by that I mean this bit column. I would expect if you want something set, you just set the bit in that column.

Attached File  AtariSDMCRL.png   12.28KB   10 downloads

Now, I would expect for the first four values you can only have ONE option set. So, if I want a wide playfield then I need to inject the decimal 3 into that address.  The default value I see used in lot of the examples uses $22 (‭00100010‬). In this case, this seems like this sets it to Standard PlayfieldEnable instructions to fetch DMA.


Could someone please clarify this better for me?



Strange issue with 800 memory cards

Sun Oct 14, 2018 12:58 PM

I've got a couple 800's. One works fine and the other doesn't so I figured I'd start to do some troubleshooting. I took out the the 3 16K carts &1 ROM board from the non-working machine and replaced all of the bare cards in my working 800. Turn it on and I get a black screen. Great, I have a bad RAM card...but which one. So, one by one I added the cards.

Just an FYI. Since one 800 has bare boards and the other has the RAM/ROM in cartridges, I'm going to call that out so you'll know which RAM I am using.

  • Put the 16K cartridge in the second slct(1st one has the ROM cart) and IT WORKS.
  • Put the 2nd 16K cartridge in the third slot, IT WORKS
  • Put the 3rd 16K cartridge in the 4th (and last) slot, BLACK SCREEN
  • Remove the 16K cartridge from the 3rd slot and replace it with the 16K cartridge from the 4th slot. The forth slot is now emptyIT WORKS
  • Put the 16K cartridge I took out and put it in the forth slot BLACK SCREEN.
  • Take out the 16K cartridge in the last slot and replace it with a 16K board. IT WORKS.

So, I'm a little confused. I've proven that all 16K cartridge are good but the machine will not start up if I put a 16K cartridge in the last slot but putting a 16K board in the last slot is completely fine.



Any ideas?