4 ms·

UP9600: How to Bit-Bang 9600 Baud RS-232 on the C64

• Scoundreller 5y ago
  > TTL-level RS-232 I ran 115k2 for a couple years directly between an atmel 8515 (sending TTL) and a Pentium2 motherboard (sending +12/-12) 24/7 for a couple years with no ill effects.
  • monocasa 5y ago
    atmels are known to be tanks wrt to overvoltage protection. IMO half the success of the arduinos is that their atmel's pads can even handle children. Few chips are so tolerant.
  • snvzz 5y ago
    Least you could have done is a voltage divider with a couple high value resistors.
• snvzz 5y ago
  This is a very cool way to actually use the CIA's serial port. But this also means it is technically not bit-banging. Ironically, bit-banging is what the C64's "KERNAL" does by default in its rs232 implementation.
• johnklos 5y ago
  Interestingly, the 6551 (and later 8551) are used on the Commodore Amiga A2232 seven port serial card. Seven of them are run by a 3.58 MHz 65CE02 at up to 19200 baud, although the card can be modified to run all ports simultaneously at 57600 baud, or two ports at 115200 baud. Because the 65CE02 does all the work, there's almost no overhead for the host Amiga. It's a versatile chip! The fact that the C64 and friends can emulate a 6551 is impressive. That they can emulate it up to 9600 baud with unused shift registers, on the other hand, is awe inspiring.