Old chips for new project.

From: Chuck McManis <cmcmanis_at_mcmanis.com>
Date: Tue May 15 16:11:29 2001

> > there have any advice/suggestions???

I missed the start of this thread, however if the trick is to build a
microcomputer from scratch then I can suggest two possibilities:

    1) Build it around a '5 chip' computer.
            Z80, Z80-CTC, 2816 EEPROM, 6116 2K RAM, Z80-DART
        You will need to add a 2Mhz TTL "can" oscillator
            a MAX233 TTL->RS232 signal level converter
            a 5volt regulator

I can supply you with a nice 2K monitor that I wrote for the Z80 that lets you
dump memory, enter hex into ram, and basically have a good time with it. (I've
got both a 2K version and a moderately more sophisticated 4K version)

    2) Build it around the Motorola 68HC11 single chip processor
        The MC68HC11-E2 has 2K of flash on board and 256 bytes
        of RAM. Just add an RS-232 level shifter and 5 volts and you
        are done. Search for 'BOTBoard' to find a _really_ easy to build
        system.

> When I started out in electronics, I got one of those big bags of
> 'untested' TTL chips from Bi-Pak (IIRC). Many of those devices failed in
> very odd ways -- 7483 adders where one internal carry connection didn't.
> That sort of thing. I spent a long time trying to figure out why my
> circuits didn't work properly.

PolyPaks was famous for this. It wasn't until much later that I figured out _why_
they were so cheap. I ended up buying one of those "assortment in bins" thing for
$100 (huge budget on my part!) and had a great time with a DigiDesigner building
and using circuits.

> When you get more experienced in electronics, and have some more test
> gear, then you can start using such chips. If things don't work, you'll
> know how to trace the fault.

Gear acquistion plan:
    #1 Soldering iron
          (from this you can make a continuity tester with a lightbulb and two
clips)
    #2 Digital Multi-meter (Volts/Ohms/Amps at least AC and DC scales)
         (these are now dirt cheap thanks to single chip solutions)
    #3 Now build a logic probe, have it capture high/low and clock signals.
        Next build a simple TTL level input frequency counter.
    #4 on my must have list is a decent power supply, you can build
       one from a kit or buy one, don't skimp, get at least 5v, preferably
       three supplys (two adjustable) to be able to do split supply things
   #5 on my "must have" then is an oscilloscope. 20Mhz bandwidth is
      fine for early TTL stuff, but you'll probably want to end up with a
      100Mhz or better scope.
    #6 build an Eprom programmer (for micro processor development)
       it is easy to build one for a single family of Eprom. Even easier if
      you target EEPROMs (no UV eraser needed)
    #7 is a function generator. If you are going to diagnose things you have
      to know you are starting with a valid signal. This is also invaluable
      when doing analysis of AC circuits.
    #8 is a logic analyzer or state analyzer.Once you go to far down the
      sequential logic path you will need one of these (Tony: Did you know
      Agilent has discontinued the LogicDart!?!?)
    #9 Get a x86 architecture machine for your bench. You'll probably
      run DOS on it (maybe Windows) so that you can run the free tools
      that manufacturers give away.
    #10 Schematic Capture/PCB Layout package (run it on your PC from
      step #9) there are some reasonable ones that are cheap (EZTrax is
      free for example)

At this point you are equipped to build what ever you need next...
--Chuck
Received on Tue May 15 2001 - 16:11:29 BST