(Topic ID: 221615)

Oscilloscopes and Pinball

By oldschoolbob

5 years ago


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  • 49 posts
  • 11 Pinsiders participating
  • Latest reply 5 years ago by barakandl
  • Topic is favorited by 8 Pinsiders

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    #5 5 years ago

    In order to reduce overall chip count, creative things were done with the memory map / addressing. Sometime, an address line was used only to select PIAs etc. Therefore, while you may see what look like normal waveforms on most of the address lines, others may look totally dead if your scope can't catch and display a single fast change (a single read or write to a port).

    And, as others stated, while in a repeating loop, the code may not cause lower address lines to change until it jumps outside the loop.

    #12 5 years ago
    Quoted from Enaud:

    I would get one if I could find one at 33mhz specification. I have not found one of them yet. And from what I read at Tektronix, they are not interchangeable.

    I could obviously be wrong but I would expect that the 100MHz will work just fine.

    Every few of my scopes were rated at 100Mhz and I have always purchased 100's as replacements.

    #13 5 years ago

    Wow! That P6028 is kind of old (1963-1966). I don't see any sign of a cap on the manual. Many probes you buy today have a trim cap at the base so you can fine tune the probe to the scope (scopes often have a square wave output for this purpose).

    I wonder how old my Dad's Vacuum Tube 1MHz Tektronix is I have under my bench? Talk about boat anchors!

    #15 5 years ago

    They made for a fine opening for the original B/W The Outer Limits!

    In High School Physics, the Teacher got the use of an O-Scope and Played through the entire song of Free Bird one day for us to "Watch". I guess it was his way of trying to somehow make the class more interesting (late 70's). Either than, or he was nursing a Hang Over that day.

    #22 5 years ago

    For that, you can make a NOP test cpu (6800). You lift all data bit lines (D0-D7) on a 6800 chip and tie them high or low to form a data byte of $01 (hexidecimal). 01 is the NOP (no operation) command for a 6800.

    The Cpu resets, goes to address FFFE and pulls the first half of the 16 bit POR jump address. Increments to FFFF and pulls 2nd half. Jumps to $0101 and pulls the first command byte which will be a $01. 01 says do nothing except increment program counter and get next byte. Which will again be 01. Repeats forever. So, you end up with a 16 bit counter as it counts from 0000 to FFFF and rolls over.

    That will give you a steady waveform.

    #25 5 years ago

    It really sounds like you need to get an old book from the late 70's about Programming Micro computers.

    It sounds like you are thinking along the lines of a "program" that is running in a higher language. The 6800 is using what is referred to as machine language. The "C" in cat, exists in memory as an ASCII byte. It takes many line of code to go fetch that byte and then transfer it to an external device, usually through some kind of an I/O port. If it needs to go out to a serial device (a single transmission wire), it has to shift it out one "bit" at a time, which would require a loop of code.

    Almost no way to see a fixed pattern with a scope. Read up on signature analyzers to see how a tech would trouble shoot a running circuit. And even then, it requires you lock the program into a know mode or condition so you know what "should" be happening as opposed to what actually is happening.

    A0 through A16 form a 16 bit address word which is used to point to one specific byte in memory. D0 through D7 contain the data byte that is either going to be written or read from that memory location.

    #44 5 years ago

    And you realize this is what you are looking at:

    Address line:
    76543210

    00000000
    00000001
    00000010
    00000011
    00000100
    00000101
    00000110
    00000111
    00001000

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