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stepho

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    Old cars, computer history

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  1. I'm a bit late to the party - oh well... @Andrew Davie's bit twiddling reminds me of DEC's radix50 method to pack 3 characters (selected from a set of 40) in 16 bits. See https://en.wikipedia.org/wiki/DEC_RADIX_50 Relies on cheap multiplication to pack them and cheap division to unpack them. Packed format was essentially char*40*40+char2*40+char3 Each character takes log(40)/log(2) = 5.32 bits. I used it on an ARM project a couple of years ago where I had to send text in very small radio packets between 2 devices. The reduced character set was adequate for my purposes.
  2. If going the USR route then you could have a simple assembly routine that simply does the AND #01 instruction to get the lowest bit. No FP required.
  3. x MOD 2 just returns the lowest bit: 0 or 1. Replace with x/2<>int(x/2) Sure wish Atari Basic has bit operators. I agree with Rybags, probably meant to be (D-2) MOD 2 and (D-1) MOD 2. Except that (D-2) MOD 2 is always exactly the same value as D MOD 2 . (2 MOD 2) is of course just 0 and (1 MOD 2) is always 1 .
  4. For me in the late 80s and 90s on non gaming devices, I'd build my binary on a DOS based PC, burn the image to an EPROM, plug the EPROM in and see what happens. Also had a big pile of EPROMS being erased under a UV lamp. A RAM based EPROM simulator certainly would have made my job much easier - oh well, 20/20 hindsight. My equipment was modified to have a bank of LEDs hanging off it that my code would trigger on/off as it passed through various points (eg turn on LED3 when entering interrupt handler, turn off when exiting handler, or turn on LED5 when a particular state is reached). I'd hook up an oscilloscope to these LEDs, record a run and look at the recording to see the timing and which routines/states were being reached. I still use this technique for time sensitive code that can't be single stepped with a modern debugger (typically when my code is watching external signals that can't be slowed down).
  5. Since we mostly want to store frequency, volume and modulation effects, that's a pretty good match for MIDI.
  6. Sandbagging came from drag racing. Run the early part of the day with a bag of sand in the car, hidden from prying eyes. For the final race, secretly remove the sandbag. This works because to go faster you have to overstress the engine. Going faster means risking the engine blowing up, which would lose the race. If you think your opponent can do a 5 second run then you stress your engine to do a 4.9 second run. But if he removes the sandbag then he can do a 4.7 second run and win. You can second guess him by stressing your engine even more but if he hasn't used a sandbag then you have stressed your engine more than it needs and maybe blow it up when you didn't have to.
  7. Australian spec 2600s output to VHF channel 3 or 4. We didn't have UHF stations at all in the early 1970s and only the more expensive TV's had UHF receiver channels in anticipation of it coming soon.
  8. Might be useful to remember what BCC and BCS stand for: BCC - Branch if Carry is Clear (ie previous operation did not require a carry) BCC - Branch if Carry is Set (ie previous operation did require a carry, typically) CMP is really just SUB that throws away the results but keeps the flags. So CMP XXX is really SUB XXX, which is really (reg A - XXX).
  9. From the image, the part number is CO14806-12. As pseudografx said, 8302 is the production date.
  10. If the VR is getting way too hot then it is probably shorting something. Be careful that you don't replace it and then simply fry the new one too.
  11. Wasn't that based on this thread? https://forums.atariage.com/topic/330879-16k-3d-engine/
  12. Cool ! My uni used Compucolour as terminals to the VAX VMS systems. First week at uni they gave us am 8" floppy and a few minutes of "insert disk, turn on, press '1', then login" for the less bright among us. Not many students realised that there was a full computer inside it.
  13. At school (8th grade) we had dial up access to a PDP-11/45 running Basic+. Later the school bought some CP/M machines for which I wrote a Z80 disassembler and some machine language graphic routines. Then in Uni I moved up to big iron - DEC-10, PDP-11/70, VAX-11/750 and an IBM 360. But I bought myself a second-hand Atari 800+1050 and used it to prototype a mini payroll package for my Pizza shop boss (first paid SW job). Handed in my third year uni project printed by a 1020 plotter (ie half width and half height of standard paper but still 80 column).
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