13 Nov
2005
13 Nov
'05
2:42 p.m.
Subject: semi-homemade micro
From: compoobah at valleyimplants.com
Date: Sun, 13 Nov 2005 11:22:23 -0600
To: <cctalk at classiccmp.org>
All the talk about building a mini from TTL got me thinking about homebuild
micros, and what one would look like if I decided to build one
(been playing with my IMSAI, too, which probably accounts for some of it)
=0D=0A
Using RTF??
RISC would be out, due to difficulty of assembly
coding,
and 8086 seems a bit dull.
Z-8000, TMS9900, and RCA1802 seem unavailable, and 6120 doesn't
have many registers.=0D=0A
The 1802s are available as is the 6120 (spare time gizmos has kitted both).
(Harris makes the 1802 and 6120.) old 1802 can be salvaged from EFjohnson
made VHF mobile radios of early 80s vintage and 6120s from defunct
DECmateII/IIIs.
Bob Armstrong [Spare time gizmos] has both the ELF2k and Embedded ELF
(1802) with an option for IDE/compactflash disk to run ELF OS. The
6120 has IDE interface and even a front pannel option. they aren't 100%
kits but all the seamingly unobtainium [PCboard, PALS/GALS, PROMS and CPU]
are covered.
Z8000 can be found but takes a bit of hunting.
The easiest source for 9900s is an old 99/4 console thats munged.
the 6120 (PDP-8 with EMA) is a great programming machine. Minimal junk
to get in the way and it has the PDP-8a dual stacks as well.
Looks like the best available ideas from an ease-of
building and
obtaining would be Z-80 (or variant), 6809, or 68000 (close to
top in complexity, esp. if a front panel is wanted).
6502 could also be a possiblity.=0D=0A
I suppose either native IDE or another system serving
as a storage
server would be the way to go, the IDE could either connect to a
old drive or a smallish CF card, and flash firmware would probably
be best, or EEPROM. SRAM seems to be the way to go for smaller
systems.=0D=0A
IDE is a easy interface for most micros and it's been put on
1802, 6120, 6502, 6809, Z80(family), 8085, TI9900, Z8000,
68000 and likely I've forgotten a few dozen.
One you didn't mention is the T-11 (base pdp-11 40 pin chip) as
these can be salvaged from VT240/241 terminals, HSC50s, RQDX1/2/3
controllers and a few other DEC boards. Interface is 8085ish and
that and 32k of ram would be a PDP11, the IO is tough as if you
wish to run DEC OS you must simulate DEC devices (some are easy).
Just wondering what the thoughts of the list would be
for specs
of a "new" hobbyest micro.=0D=0A=0D=0A
First off any cpu is reasonable. Depends on preferences, what you have
and maybe phase of the moon. Same for level of complexity.
At one end you have the COSMAC ELF with 256bytes of ram and rudimentary
front pannel simple and inexpensive. At the other extreme some of the
Z80 flavors like the P112 (everything including the kitchen sink).
Then there is do you want a bus or no, expansion or no, fully loaded
or just minimal.
I consider 1802 8085, z80, 6502 and 6800/6809 all very easy to use and
interface. Even the TI9900 is not to bad if you have the clock
generator chip [9904]. Believe it or not the 68000 is fairly
straight forward and only bit worse than 6809. the Z8000 is hardest
of the ones mentioned as the bus is more complex.
For most a front pannel adds significant complexity, notable exception
is 8035 (8048) and 1802.
If I'm doing Z80, I pretty much expect to run a language in rom or OS
such as CP/M. with those in mind the must haves are:
Z80, z180, Z18x
RAM at least 32k (more is good)
boot rom
2 serial ports Console and link to PC for download.
1 Parallel port for printer
some kind of mass storage (Floppy, IDE, CF, Flashram)
However you really asking an open question with no direction given.
Allison