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Thread: Wire wrap

  1. #1
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    Default Wire wrap

    While researching wire wrap ran across this illustration of the backplane of a PDP-8I. https://en.wikipedia.org/wiki/Wire_w...-backplane.jpg

    OMG.

    -CH-

  2. #2
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    Looks like cheap threadbare carpet.

  3. #3
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    Hah, yeah, big wire wrap boards can be a bit...intimidating Some of those big ones are done with automatic or semi-automatic machines.

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    But I have seen wire wrapped old machines that had more order than this image. The PDP-1 that demos "Space Wars" at I forget which computer museum for example. When they show the back, sure its a maze of wire wrap but it isnt all the same color and has some uniformity to it all. Maybe that is the hand wrapped example and this pdp-8I is machine wrapped.

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    I still occasionally do wire-wrap prototyping. The problem with the rat's nest look is that both manual and automated wire wrapping systems select from a menu of stripped, fixed-length wires, so the appearance looks untidy. I've got a couple big ECL boards that look even worse because they use twisted-lead wires for differential signaling.

    That being said, wire-wrapped boards can be made to be extremely reliable and can, in a lot of cases, outperform printed-circuit boards because the signal length can be accurately controlled.

  6. #6

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    Wire wrap also has much less cross talk. With pc board prototyping tools today it is much easier to make a board and not worry about learning to make proper wraps.
    Dwight

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    ...and I'll state the obvious: It's much, much easier to modify a wire-wrapped board than a printed circuit board. Heck, you can probably redesign the board just by unwrapping and re-wrapping.

    Too bad the technology isn't used much today. I think it was Western Electric that pioneered the idea of wrapped gas-tight connections. And you know how much of a stickler the old Bell system was for reliability...

  8. #8
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    Quote Originally Posted by Chuck(G) View Post
    ...and I'll state the obvious: It's much, much easier to modify a wire-wrapped board than a printed circuit board. Heck, you can probably redesign the board just by unwrapping and re-wrapping.

    Too bad the technology isn't used much today. I think it was Western Electric that pioneered the idea of wrapped gas-tight connections. And you know how much of a stickler the old Bell system was for reliability...
    From what I read about the topic, the silver-plated wire actually cold-welds to gold-plated pins and seals out oxidation. Pretty remarkable.

    The thought of an automated wire-wrapping machine (and the poor guy who has to program it) distends my cranium, however.

    -CH-

  9. #9
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    Not only does it cold weld (when you use a proper tool with the proper wire), but silver oxide conducts nearly as well as silver. That's why it's used in switch contacts, too.

    I still wire wrap, both for repairs and for prototypes where there's a lot of uncertainty about a new design, especially if there's going to be a lot of parallel data/address bussing. If I'm only making one or two of something, the wire wrap prototype may end up being the final version.

  10. #10

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    Quote Originally Posted by Chuck(G) View Post
    ...and I'll state the obvious: It's much, much easier to modify a wire-wrapped board than a printed circuit board. Heck, you can probably redesign the board just by unwrapping and re-wrapping.

    Too bad the technology isn't used much today. I think it was Western Electric that pioneered the idea of wrapped gas-tight connections. And you know how much of a stickler the old Bell system was for reliability...
    As a 42 year veteran of the "All Bell and No System" that disappeared at the end of 1983, I can vouch for their love of wire wrapping entire backplanes. In a #1AESS, the CC (Central Control -- what we now call a CPU) measured approximately 3 feet wide and 7 feet high. Rather than one single backplane it had about a dozen that spanned the width of the frame and were stacked vertically. All were wire wrapped with yellow 30 gauge wire. Something I had never seen before or since was the use of white 30 gauge coax to run connections that went from one backplane to an adjacent one above or below it.
    "It's all bits on the bus, Cowboy! It's all bits on the bus!" -- Tom Beck, #1ESS Instructor, Southern Bell Opa Locka Training Center

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