PCB vs perfboard construction economics (was Re: "New" PDP-8)

From: Ben Franchuk <bfranchuk_at_jetnet.ab.ca>
Date: Tue Apr 2 11:40:42 2002

Richard Erlacher wrote:
> What I've encountered more and more is the inconvenience associated with
> trying to use current-generation components in wire-wrap. I'm always having
> to build adapters that make a DIP out of a TSSOP or the like. The adapters in
> a prototype often exceed the cost of a PCB. It's much easier to build small
> boards, about the size of a typical playing card, and that's enough space to
> house a microcomputer of reasonable capability, comparable with any "classic"
> 8-bitter of the '70's and '80's, including its I/O, memory, video, and mass
> storage interfaces. After I get the current task off the table, I'll take a
> closer look, but it seems to me that it's easier to put a system on a
> playing-card sized board, and cheaper too, using current technology, than to
> recreate the old stuff using parts that are increasingly scarce and boards
> that are needlessly large and costly.

I would suspect that one would need a larger size PCB because that size
of PCB can't hold things bigger than 56? pins. A reasonable CPU just
fits in a 84 pin PLCC. Somebody (link not handy) makes a PLCC to
breadboard adapter on the net, so you can use a breadboard for the newer
(small) chips. It is the speed of the old I/O chips that are a problem.
A 1.5 Mhz+ chip is high speed and all the good chips like floppy disc
controllers are all in a mother board chip set for a PC. Mind you 8 bit
CPU's are limited to 64kb as we all know is way to small for something
other than a minimal PC.
My own CPU design (in a FPGA) is limited to 512kb of addressing range if
I want to emulate a fictional CPU in a 40 pin dip. While I use 32kx8
static ram and few special control signals and a UART in the FPGA most
of my design is what a possible 1980's cpu could have been like: Limited
front panel, Serial I/O, Dynamic Ram,Mother board with CPU.

Ben Franchuk - Dawn * 12/24 bit cpu *
Received on Tue Apr 02 2002 - 11:40:42 BST

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