Subject: [stella] Reverse engineering the TIA (Was: Midified VCS...) From: Oliver Achten <achten@xxxxxx> Date: Thu, 6 Dec 2001 11:20:29 +0100 (MET) |
Hello Mark! I intend to redesign it using 74xx IC's (don't laugh...) . Preferably F-Types. Well, i looked at the counters, and they indeed consist of 6 self-feedbacked shift registers, driven by a two phase clock , using some kind of wired-and logic to decode various states. Fortunately, J. Miner wrote at the H-Sync counter, which number causes some kind of action (H-SYNC start, etc.) The H-SYNC counter is clocked 1/4 the clock of the master clock (3.58Mhz). Once I figured out in what order it counts, this counter could be replaced by a standard binary counter, since it really is not important in what order the H-Sync counter counts (as long as your supply logic decodes the same states...). Unfortunately, this is not valid for the player counters (because of the sideeffects)..... The bus logic and sync decoding are not really a problem to do in TTL. The Playfield registers are tricky. Could be replaced by latches and a flip-flop chain, which is logically anded with the outputs of the latches. The H-Move counters... Any idea? Well... Lets go to the next sheet... ;-) Sheet 2 consist mainly of the Bus drivers, the collision detection, and the address decoding. The adress decoding consist again of primitive wired and logic. TO do it in an FPGA, you'll have to convert it to real AND gates (which will significantly increase the gate count). I intend to use 4 plain 74154 4 to 16 address decoders... (yuck). The next 2 sheets consists of the player-missile-ball, etc logic. In the last sheet, there are 4 7-bit registers for the color data. Above is the priority logic, which selects the color register. My prototype will have the color phase delay logic replaced by two PROMS, where the colors are hardcoded (as i said). Well, thats how far i've gotten until today.... Tschuessi Oliver -- GMX - Die Kommunikationsplattform im Internet. http://www.gmx.net ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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