Vicious - Sound Card for the Apple-1 Computer
Hello and welcome to checkout this project on mine which is about creating a sound card for the legendary and pioneering home computer of the seventies, the Apple-1.
Current status now, on April 2014, is that the first and the only prototype of the sound card exists with the features explained in this page. Some fixes and changes need to be done to the circuit board and next version of the circuit board will be manufactured soon. I sure hope it's going to be the final version because is not that cheap fun.
- SID Chip for sound generation. SID is the sound chip used in Commodore 64.
- CIA Chip for timed interrupt generation. Without timer there could be no rhythm. Timer can also be used for other applications. For the next version I'll try to fit in pin holes for CIA chip's input/output ports. For example a joystick could be connected there. And don't ask what use might a joystick have in Apple-1. ;)
- Onboard ROM for firmware which at moment means a menu driven "Vicious SID Player" with CFFA1 card integration. I also try to fit in an API to ease software access to some of the card's features.
- The firmware on the card can be updated (EEPROM re-programmed) in-place by just moving the write-protection jumper and running the update program.
- Audible digital noise, buzzes and hums are quite low level. At least I'm happy with the result. Although nothing beats the sound of the SID chip, it cannot be considered as a hifi device in traditional sense so you'll always hear something "extra".
- Uses only the 5V power line. SID chip needs also 12V (that is for original 6581 model, 9V for the later 8580 model) but it's generated on the card from the 5V line with dc-dc step-up converter. Original Apple-1 should have 12V available, but most of the clones/replicas don't have that, mine included.
- By changing 3 components on the board, the card can host 8580 version of the SID chip instead of 6581 version, but I haven't tested that yet.
- Occupies 4kB of the computer's memory address space: $B000-$BFFF. The firmware $B000-BEFF, SID: $BF00-$BF7F, CIA: $BF80-$BFFF.
- CIA Chip's IRQ line is connected to processor's IRQ line.
- "Vicious Sid Player" is able play many of the tunes created for Commodore 64 environment, but not all. Some tunes run in an address space that is not RAM in the Apple-1. Some tunes configure interrupt generating devices themselves and there are more interrupt sources on real C64 than a single CIA chip.
- SID chip is not in the same address as it is in the Commodore 64, that's not even possible, so tunes and for example sound generating programming examples need to be modified for all SID accesses. Tunes are modified automatically by Vicious SID Player and it has worked surprisingly well but the method is not 100% reliable.
Will be decided later. If you want to be kept informed, drop me a line in my gmail address. That's with the prefix "sampo.peltonen". In any case I cannot supply SID or CIA chips, you'll need to find those from somewhere else.