Subject: Re: [stella] TIA video timing From: Adam Wozniak <adam@xxxxxxxxxxxxxxxx> Date: Thu, 10 Mar 2005 04:09:49 -0500 |
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Thu, 10 Mar 2005, Chris Wilkson wrote: > Errrrmmm...no. > > sync should be 16 cycles wide, not 68. blank should be 68 cycles wide. > I don't remember the *exact* relative timing at the moment, but I think it's > like this: > > begin hblank (wait 16 cycles) > begin hsync (wait 16 cycles) > end hsync (wait 36 cycles) > begin active video (wait 160 cycles) This may be a better reference: http://www.cuddlepuddle.org/~adam/fpga2600/TIA_HW_Notes.txt It shows them setting hsync at 16 and clearing it at 32. It shows them setting hblank at 224 and clearing it at 64. > The /sync pin is hsync xnor vsync, like you have it below. > The /blank pin is hblank nor vblank. > Both pins are active low. So now I'm thinking: -- posNOW is a 8 bit counter, that goes up from 0 to 227 -- regVSYNC is bit 1 of TIA register address VSYNC -- regVBLANK(0) is bit 1 of TIA register address VBLANK -- sync is the sync output pin of the TIA (pin 2) -- nblk is the bl output pin of the TIA (pin 6) -- video sync output process (posNOW) begin if posNOW = "00010000" then -- 00010000 == 16 sync <= not ('1' xor regVSYNC); elsif posNOW = "00100000" then -- 00100000 == 32 sync <= not ('0' xor regVSYNC); end if; end process; -- video blank output process (regVBLANK) begin if posNOW = "11100000" then -- 11100000 == 224 nblk <= not ('1' or regVBLANK(0)); elsif posNOW = "01000000" then -- 01000000 == 64 nblk <= not ('0' or regVBLANK(0)); end if; end process; Did I get the logic levels right? Ack, I still don't feel like I'm on solid ground here. > Clever use of overflow to get weird counts like 68, btw. > The counts above work well with this scheme...it's why they > chose the numbers they did. Cheap as possible!!! Thanks. :) - -- adam@xxxxxxxxxxxxxxxx http://cuddlepuddle.org/~adam KG6GZR http://cuddlepuddle.org/~adam/resume.html "Feminist? Why would I want to alienate half the population? I'm an egalitarian." -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.1 (GNU/Linux) iD8DBQFCL/1ryvXf5Z0z5zERAsVdAKCi8E7Rd0SwxuBRNEsj8vRufhZ+bACfZlQJ 9eKb/5uWiPzxqHoLqSolzxQ= =aLvG -----END PGP SIGNATURE----- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://stella.biglist.com
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