Subject: RE: [stella] Cartridge read timing problems? From: "Pension Maricel" <Maricel@xxxxxxxxxx> Date: Tue, 20 Apr 1999 09:18:29 +0200 |
See our web page Pension Maricel C. Tacó nº 13 Sitges 08870 España Tel. 938-943-627 Fax 938-943-869 HTTP://WWW.MILISA.COM Maricel@xxxxxxxxxx -----Mensaje original----- De: Mark De Smet <desmet@xxxxxxxxxxxx> Para: stella@xxxxxxxxxxx <stella@xxxxxxxxxxx> Fecha: martes 20 de abril de 1999 2:20 Asunto: [stella] Cartridge read timing problems? > >If many of you recall, I'm working on the great atari development >system/game server. Currently, mainly on the game server. > >I am having slight quirks, and maybe someone out there may know why. > >The hardware: >Attached to the atari bus(the A+D line out of cartridge socket), is a >screensaver ROM(it is just an atari rom that John Harvey wrote for me), >and the output of a octal 3-state buffer.(I'm using a 74HCT541) The >address lines go both the the screensaver ROM, and into a MUX(3x 74HCT157. >The output of the address mux's and the input of the 3state buffer go to a >couple other roms(and later other stuff). It is configured so that only >the screensaver, or the buffer reacts to the atari's reads(atari A12). >When setup for the screensaver, runs fine. when setup for the other >roms(through the 3state buffer & MUX's), only 'mostly' runs. In this >state, the output of the 3 state is only enabled when the atari reads(and >in this state), and the mux's select the atari address input to be passed >on to the other roms. > >What happens: >The ROMs are currently a pile of 'commerial' software. The problem is >that the games run improperly. All games at least start up. Some games >seem to run, and crash later. Others display wierd graphics. For >instance, Adventure, the power up screen looks like this: > >################# >#x x# >#x x# ># # ># # ># 1 # ># # ># # ># # ># # >####### ####### > >where the x's are a patch of boarder that appears and dissapears. It >flickers on and off irratically. Boths sides flicker at exactly the same >time, but it does not appear to be periodic. The patch is exactly the >same width as the edge(2 playfield blocks, I think). > > >I believe the problem has to do with the 3 state buffer(the other rom's >are 150ns, and should be plenty fast enough). When changed to an ALS, >games by and large behave better, but still crash and have funny graphics >problems. My best guess is that because the atari doesn't give the >cartridge a real read signal, but instead just makes the cart(and hence my >buffer) base it's output on the address, that my buffer happens to either >hold the lines driven too long, or more likely not long enough. > >Any ideas about timing? >Any ideas about what else may cause such software actions? > >Mark De Smet > > > >-- >Archives (includes files) at http://www.biglist.com/lists/stella/archives/ >Unsub & more at http://www.biglist.com/lists/stella/ > -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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