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Hello! I'm wondering of anyone has investigated the feasibility of modding a 2600 so that you can switch between clock frequencies and/or color palettes. The goal of such a project would be to play cartridges of differing regions on the same machine. I've seen a similar project on a Commodore 16 where the clock crystal was replaced with an Arduino, the latter programmed to output different selectable frequencies to produce a signal for PAL and NTSC video. As for the color palette, I believe that would require a swap of the TIA chip, which could be done manually if the board is socketed. I haven't studied the schematic, and a cursory search doesn't show anything useful. To anyone with the hardware experience, do these ideas seem sound? My assumption is that the only difference between a PAL, NTSC, and SECAM 2600 are the clock crystal and TIA since the game cartridge does all the video synch. Steve Guidi
Hi All, Seriously, I have no idea what is happening here. I am working on a TURBO BASIC program that will let the user exercise their (relative) ear. It is planned to test intervals melodic and harmonic and probably a few other things. To come as close as possible to the wanted frequency (I have really a sensitive and precise ear) I use 16-bit pokey registers in stead of 8bit. Downside is that I only can play 2 tones together, but ok... Perhaps I might decide later to go to the 8bit 4# voice capabilities of pokey. Earlier today I found that DSOUND 0,4020,10,10 would produce a perfect 220Hz A and and DSOUND 0,2008,10,10 would produce a perfect 440Hz A. I was very happy with the results, I saved my program to disk and that was that. Now I fired up the Atari with Turbo Basic and I was playing again with the DSOUND command and I was not as satisfied as I was earlier today. I was like: hmm it is not right. So I started playing again with it and I found different values. After checking: DSOUND 0,4028,10,10 gives the perfect 220Hz A DSOUND 0,2017,10,10 gives the perfect 440Hz A DSOUND 0,1001,10,10 gives the perfect 880Hz A Ok it is not really a big difference, but still, I was not as close as I would have thought. So my 2 questions are: How stable is this anyway? Can I assume that pokey in 16bit modus produces a steady frequency or does it fluctuate (when colder/warmer) or is it a different part on the PCB that might have influence on the frequency? (Like the audio-out circuit)? I am using the speaker of my television set, so it is not directly what comes out of pokey. In the Turbo Basic Manual by Wil Braakman I read a formula: "de berekende frequentie in HERZ nu 1789790 / (2*freq+14) bedraagt. De frequentie bedraagt dan 16 bit (0 . . . . 65535)" (Braakman, 1988, p. 3-36). This means that the 16bit pokey value for 440Hz would be: 1789790 / (2*440+14) is approx. 2002 which is closer to my earlier find of 2008, and than my newer find of 2017. It seems that either this formula is wrong, or my ears/tuner-app. My personal findings using ear and tuner-app come way more close to 220Hz, 440Hz and 880hz than this formula. Is there a better formula somewhere? Or is there something else wrong? Or do I ask too much of a formula anyway? I am really interested in this stuff, I hope someone can help. Marius -- Braakman, W. (1988). TURBO BASIC XL 1.5 MANUAL. 's-Hertogenbosch, Netherlands: Stichting Atari Gebruikers.