4 ms·

What a fun paper computer! I wonder if those cards still exist somewhere.

anonymousiam 4y ago
Good question. You inspired me to see what I could find. The instructor was still associated with the college as of 2015, but he may have retired now. Google shows nothing associating him with 6502. I expect that the course curriculum has changed in the last 43+ years. A little cyber stalking shows that he sold his house in 2017: https://www.youtube.com/watch?v=inCBLQJja2U https://www.youtube.com/watch?v=inCBLQJja2U While thinking about him and the course, I remembered my final exam in that class, which I nearly failed. I had mastered the material maybe a little too well. The assignment was to program our KIM-1 (https://en.wikipedia.org/wiki/KIM-1 https://en.wikipedia.org/wiki/KIM-1) to drive a speaker with a 1KHz square wave on a PIO port (bit 0) when a switch was closed between ground and the same PIO bit 1. So obviously you had to set up the data direction register of the PIO with bit 0 as output and bit 1 as input, and have a loop that would toggle the bit 0 output every 500us if the PIO bit 1 input was at logic-0. Even back then, I liked to optimize my code, and the instructor did not give us detailed requirements about the state of PIO output bit 0 when PIO input bit 1 was logic-1, other than to say that the tone would not be present. So instead of reading PIO bit 1 in the loop and performing a compare to branch one way or the other, I simply inverted PIO input bit 1 and stored it into the data direction register for PIO bit 0 on every loop iteration. Thus the tone would be present when bit 1 was at ground, but not present otherwise (because bit 0 had been defined as an input rather than a output, and was in a high impedance state). The instructor looked at my code and gave me a "F". I had to confront him after the class and he grudgingly changed my final grade to a "C".
- krallja 4y ago
  I don’t see the problem with your code?

Good question. You inspired me to see what I could find. The instructor was still associated with the college as of 2015, but he may have retired now. Google shows nothing associating him with 6502. I expect that the course curriculum has changed in the last 43+ years. A little cyber stalking shows that he sold his house in 2017: https://www.youtube.com/watch?v=inCBLQJja2U https://www.youtube.com/watch?v=inCBLQJja2U While thinking about him and the course, I remembered my final exam in that class, which I nearly failed. I had mastered the material maybe a little too well. The assignment was to program our KIM-1 (https://en.wikipedia.org/wiki/KIM-1 https://en.wikipedia.org/wiki/KIM-1) to drive a speaker with a 1KHz square wave on a PIO port (bit 0) when a switch was closed between ground and the same PIO bit 1. So obviously you had to set up the data direction register of the PIO with bit 0 as output and bit 1 as input, and have a loop that would toggle the bit 0 output every 500us if the PIO bit 1 input was at logic-0. Even back then, I liked to optimize my code, and the instructor did not give us detailed requirements about the state of PIO output bit 0 when PIO input bit 1 was logic-1, other than to say that the tone would not be present. So instead of reading PIO bit 1 in the loop and performing a compare to branch one way or the other, I simply inverted PIO input bit 1 and stored it into the data direction register for PIO bit 0 on every loop iteration. Thus the tone would be present when bit 1 was at ground, but not present otherwise (because bit 0 had been defined as an input rather than a output, and was in a high impedance state). The instructor looked at my code and gave me a "F". I had to confront him after the class and he grudgingly changed my final grade to a "C".

krallja 4y ago
I don’t see the problem with your code?