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Thread: Silly Address/Data LED front panels on 80s machines.. or are they?

  1. #21
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    Howso? I've programmed bare iron in machine language with no LEDs. Of course, you need some sort of I/O to satisfy the basic function of a computer.

  2. #22

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    Quote Originally Posted by Chuck(G) View Post
    Howso? I've programmed bare iron in machine language with no LEDs. Of course, you need some sort of I/O to satisfy the basic function of a computer.
    Because having another computer to feed information to it otherwise is more than the bare minimum, and more than what is necessary.

  3. #23

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    The Hero Jr robot has a row of red LED's on the data bus, these get modulated by either its voice (based on the Votrax SC-01 IC) or any of its sensors for light and sound that are in use. It is actually quite handy visually for calibrating the sensor's range over 0 to 255 etc. So "blinking lights" in some simple computer systems can have their utility value, plus they look cool. Here is an article about the robot, you can see the 8 red LED's on the top and the green power LED:

    http://worldphaco.com/uploads/SAVING...dio_Board..pdf

  4. #24
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    I'm sorry; I must be dense. I don't follow. You need an input device of some sort and you need an output device of some sort. What does machine code or assembly or LEDs have to do with it? You sit down with a piece of paper, and code the binary up.

  5. #25

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    Quote Originally Posted by Chuck(G) View Post
    I'm sorry; I must be dense. I don't follow. You need an input device of some sort and you need an output device of some sort. What does machine code or assembly or LEDs have to do with it? You sit down with a piece of paper, and code the binary up.
    Switches are input, LEDs are output. You input machine language directly on the switches (no assembly). This is the most basic way to enter machine language directly to a computer. You must have done this, or at least seen it done. I've got hundreds of hours doing it. Most of the time though I've used equivalent systems with a keyboard matrix and 7-segment display. The only difference is that you work with hexadecimal this way instead of octal.

  6. #26
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    Sure, but before I ever did that, I punched my machine code into cards or entered it on the console typewriter. On the CDC 6000, the bootstrap was entered by means of a toggle switch matrix, but no LEDs or lamps on that.

    LEDs or lamps are not a necessity. They're just convenient because they're cheap.

  7. #27

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    My first computer was a Poly88. It only had two lights and 2 switches. One was power and a light. The other was a reset button. It also had a light but I don't think I ever thought about what it was for?? The Poly88 had a ROM based monitor. I used it to enter code many times but working more directly with 8080 machine code I'd have liked to be able to switch back and forth from Hex to Octal. Hex is better for addresses and Octal is better for 8080 machine code.
    Now I advance many years I find an IMSAI with disk drives for cheap. There is no software that I can find for it so, I need to bootstrap it to running. The front panel was what I had. I toggled in a few programs to test thing like the RAM. I found this to be quite difficult to do much without some errors.
    I needed to make faster progress. I wrote a simple serial transfer program. We are talking about a real simple serial. I just needed something to go from a PC or laptop to the IMSAI. It didn't need protocols or error checking. I was only going a couple feet. Luckily, the early serial chips were configured by jumpers. It only took a few bytes of code to read from serial and place the data in the next sequential address.
    Other than a small amount of code and being able to toggle in an address, the front panel was now not as cool as I originally though. Had I given it any thought, it would have been quicker to make a little more capable serial and put it on EPROM. Something with a simple protocol, like a cassette data but with one large block of data and no error checking. Write, Read and Go are about all it needs.
    I've since found that if a system has a place for removable ROM, a EPROM is the best way to get into a system. If the processor is working at all, it is also the best way to debug.
    So, although the switches and lights are cool, they are really a waste of space.
    Dwight

  8. #28

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    Just like a hand crank on the front of a car. Who needs that when you always have a working electric starter, a good battery, a battery charger and a way to power it, and a tow truck at a moment's notice. That crank is useless. What were they thinking?

  9. #29
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    I'd liken LEDs more as an output device--i.e. a tachometer on a car. You don't really need one.

  10. #30

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    Except that you can't feel, hear, and smell a CPU running. If you haven't got LEDs, you'd better have otherv means of output.

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