Electronics Nostalgia (page 2)
~1980: Z80 Computer.
This was back in the days before switching power supplies; the power
supply was 8V unregulated, and each plug-in card had individual regulators
for +5 volts (and +/- 12 and -5v, if required). The C-core transformer
was popular at the time; note how unconventional it looks. This model (JT-249)
was made by Jones Transformers in Sydney, and was sold to me by Zero-One
electronics (where I worked most Saturday mornings while at University).
It also powered my 2650 based computer, which preceeded the Z80.
~1980:
Decwriter
Dot matrix printers were all that were affordable; about the only other
print technologies of the time were band printers, daisy wheel and golf
ball printers. (Much earlier than dot matrix was the typewriter style printer.
Before the Decwriter I used a Baudot printer, which interfaced (and printed)
at 50 bits per second, using a 5 bit code. It was last fumigated in 1945).
Many computers did not have video terminals (later to be called glass teletypes);
many interactive computers used teletype machines. The DecWriter, at 300
baud, was considered fast. In fact, the machine was so overengineered,
that it was capable of printing at 60 characters per second or even more,
so it was possible to interface it at 600 baud (and add a lot of fill characters
after every carriage return!). All I did was to change the clock frequency
to the UART chip in the Decwriter.
The keyboard on the Decwriter was very good, and it was of the standard
parallel kind that I used, so I added some extra wiring to use the Decwriter's
keyboard as the computer's input device. I made a timber platform that
went over the top of the Decwriter to put by TV set (most computers used
a standard TV set, modified for direct video input, as a monitor. 15 khz
and 50 Hz were high resolution back then!) You can get an idea of the rugged
nature of this machine by looking at the size of the stepper motor that
fed the paper:
~1982: The Great Flight Simulator Hack
See my other page for details; this is the card
that interfaced my S100 Z80 system to the Asteroids Game. If you look carefully,
you can see the FIFO chip (top right), the multiplier chips (ordinary looking
16 pin chips near the middle), the Z80-DART (Dual Asynchronous Receiver/Transmitter)
(the only 40 pin chip), the serial port connectors (top), power regulators
(top left), and bus transceivers (the 4 20 pin chips at the bottom)."MicroWorld"
was the trade name for Applied Technology, a company that was instrumental
in shaping the hobby electronics industry in those days.
This board is meant to hold wire wrap sockets, but I just soldered
the components to the board. The wires get a bit dense, as you can see,
so it's a good idea to use proper wire wrap wire (which is very thin).
I did make some proper wire-wrap projects.
The Asteroids game is one of the few that use a vector, or X-Y monitor.
These monitors do not scan in a raster pattern as does a television or
conventional monitor (left to right very fast, and top to bottom slower),
but rather trace out the image in a series of straight lines. This requires
current-drive of the deflection coils (the magnetic strength, and hence
deflection from the center of the screen is proportional to the current
through the coils). You can see the large "Darlington Power Packs" bolted
to the large heatsink below. The high voltage for the anode, usually derived
from the horizontal deflection circuit, is in a separate cage at the lower
left (note the black high tension lead, with the large rubber circle at
the end to prevent flashover to earth). The small printed circuit board
with the seven pin socket sits on the back of the picture tube (not shown).
~1983: Battlezone game
Another famous game using a vector monitor was BattleZone, also made by
Atari. This was the first game to use bit slice processors to do enough
three dimensional calculations to make a real time perspective display.
I bought an old standup Battlezone game with the idea of disassembling
the game's eproms, but never got around to it. Now you can get versions
of Battlezone that run on your PC, but somehow the feel isn't the same.
At least I got to play it a bit. But after a while, it became quite unreliable,
and I pulled it to bits. Here is one of the boards; note the rugged simplicity!
1987: Amiga Computer
I resisted changing to Wintel computers as long as possible. In the late
1980s, IBM compatible computers had woeful CGA graphics, and Amigas could
do amazing things like 4096 colours at once! I started with an Amiga 1000,
and ended up with an Amiga 2000 with an 80286 plug-in card. They were sure
fun times. A friend wrote an excellent disassembler inspired by Z80 "resource"
(which I co-wrote; Z80 resource was inspired by the original CP/M resource
by Ward Christensen, of XMODEM fame). This disassembler, which may still
be available, was the best and fastest on the planet, and I used it a lot
to further my disassemling expertise.
Amigas used those new-fangled 3.5" disk drives; many of us still had
lots of 5.25" media, and 5.25" disks were at that time much cheaper than
3.5" disks. Not many people realise that whatever you can do with a 3.5"
disk, you can do the very same to 5.25" disks, since the interface signals
and speeds are the same. So I designed a little circuit to adapt bare disk
drives (3.5" or 5.25") to the Amiga (a little reverse engineering was required
here), and made a set of 5.25" disks that connected to any Amiga. Soon
other people saw the advantages (a typical disk collection was well into
the hundreds, so the several dollar difference in media cost was significant).
I ended up selling a lot of these cuircuits, and some made-up boxes with
1 or two drives as well. We started with good old reliable NEC disk drives,
as shown below.
Note the two chips (arrowed) near the back if the drive; I added these
to the NEC drives to provide a "disk change" feature (required by Amigas
but not the more popular IBM computers). There happened to be two 16 pin
chips positions (not connected to anything) on the printed circuit board;
presumably in case NEC themselves had to make such a modification! The
mods on other disk drives were less neat; often a chip was glued upside
down into an existing chip, and wires soldered
directly to the inverted chip.
Here is the circuitry to interface to the Amiga. This consisted of
"ident" circuitry (it told the Amiga that this was an Amiga formatted disk,
as opposed to a low density IBM compatible disk), and some circuitry for
passing through the signals to the next drive(s) in the daisy chain.
Eddie Matejowsky's microprocessor
page.
The University of Virginia's Computer
Museum page.
Mike's Home page.
Last modified: 30 May 1999: Links to Eddie and UVA.