Jump to content

Dennis Nedry

68000
  • Content Count

    1288
  • Joined

  • Last visited

About Dennis Nedry

Profile Information

  • Location
    Jurassic Park Visitor Center

Recent Profile Visitors

The recent visitors block is disabled and is not being shown to other users.

  1. An HD 20 emulator would be extremely useful for the Mac 512k because it does not have a SCSI port!
  2. I had to run Lord Nightmare's code and get the latest sound files. Here they are: Normal: http://sites.google.com/site/benboldt/files/Quadra%20700%20Normal%20Lord%20Nightmare.wav Easter Egg: http://sites.google.com/site/benboldt/files/Quadra%20700%20Easter%20Egg%20Lord%20Nightmare.wav
  3. I have not tried this but it seems to me that a • (option + 8 ) pushes items to the end of the alphabet and a ° (option + shift + 8 ) or a space pushes it to the beginning. It might be worthwhile to disable everything but these two extensions using Extensions Manager, including disabling all control panels. If that makes it work, you can then re-enable things until the problem reappears to identify the problem.
  4. Note that using a single transistor will invert the signal. With N-Channel: input -> output 0 -> high-impedance (open circuit) 1 -> 0 With P-Channel: 0 -> 1 1 -> high-impedance To achieve all 3 states, you would need 2 separate signals whether you use transistors or a tri-state chip. Connecting the outputs of an N and P together: n, p -> output 0, 0 -> 1 0, 1 -> high impedance 1, 0 -> 'BANG' + magic smoke 1, 1 -> 0
  5. Yes I should have mentioned that - it would be very easy to not notice. I did it that way to avoid crossing wires in the diagram.
  6. You can decode the address range 0xFAXXXXXX with 2 chips if you have a 7400 (quad 2-input NAND) and a 7432 (quad 2-input OR). This leaves one extra NAND gate.
  7. We should quantify ROM vs. paged ROM vs. RAM vs. SCSI vs. NuBus speeds. If you can get the data there fast enough (i.e. parallel ROM like dougg3's current designs), ROM should be the fastest but by how much I'm not sure.
  8. I just pulled out the datasheet for the Atmel AT90USB647: So the port values in fact affect the pull-up resistors when in the input direction. I would recommend writing all 1s to the ports to activate the pull-ups when reading. This should return all 1s whenever polling the ports with no SIMM inserted. Then just use the PINx registers to read the input values. This differs from other microcontrollers - I am used to using the PORTx registers for both reading and writing data.
  9. If information is available directly on the address/data bus, that is the fastest possible access. But it seems like there would be a lot of overhead when connecting this with serial flash memory, in at least these ways: - Extracting/converting serial data to parallel - More complicated driver, more instructions/jumps/waiting for ROM ready per read - probably others When we consider this overhead, we should compare it to the overhead of using NuBus which was originally designed for this purpose. If we hack the friggin' crap out of NuBus, we could make a mass storage card similar to
  10. 8 MB is the limit of the ROM slot, after that you have to start adding clips for more address lines, if it can work that way. Each clip would double the max ROM if the memory controller allows this. Max ROM SIMM = 8 MB * 2 ^ (# of clips) We also talked about using some sort of large flash drive/CF/SD card, but this presents a problem because they are serial and the Mac expects parallel ROM. It would be difficult to convert serial to parallel fast enough for that to work.
  11. I know enough 68k to be dangerous, but not without strict reference to the instruction set and lots of head smashing upon the keyboard. I want to chime in that the Mac Plus that I tested my HD-20 on is not known good, so there is a chance that the drive is still okay, or just a short or open or two away from it. I don't currently have the resources to delve into my Mac collection, but this may change some day soon.
  12. I don't know if a powered hub would fix that or not. I think that it would fix it if the +5V line was disconnected, though I'm not sure what would happen to the signal without a common ground if that got disconnected. Testing for power could at least give some useful clues.
×
×
  • Create New...