From: bownes@peterpan.crd.ge.com (Keptin Komrade Dr. Bobwrench III)
Newsgroups: comp.sys.tandy
Subject: Re: CPU's used in early Tandy's
Date: 27 Jan 93 21:27:33 GMT
Organization: School of Corrective Phrenology


More than you Ever wanted to know about Model II/12/16/6000's.

From article <C1Howz.nK@acsu.buffalo.edu>, by kist@acsu.buffalo.edu (james e kist):
> The TRS-80 I used the Z80 at ~1 Mhz, TRS-80 III used the Z80, but the 2.77
> Mhz model, and the TRS-80 Model IV use the 4 Mhz Z80A. What did the TRS-80
> Model II, 16, and 6000 use? Also, what was the original purpose of those
> three machines? (The Models I,III, and IV were mainly for home use. Were
> the Models II, 16, 6000 meant for business use, running networks, or what?)
> Thanks in advance for any help.

The model III was not exactly 2Mhz because of the video if I recall correctly.

The model II,12,16, and 6000 used a 4Mhz Z80, with the 16 and 6000 having
a 68000 as well. Xenix used the z80 as an io processor. In 1983.

The model II (introduced about 1978) was aimed at the buisiness market.
The model 16 (1982), answered the demand for faster COBOL machine, and with
XENIX, andwered the demand for multi-user computing in a small office.
By the time things worked up to the model 6000,  (and in fact, the mmu
upgraded 6000) 8 users could be supported, 2-4Mb of main memory, and 280Mb
of disk.

The only difference between the model 16 and the model II was the
addition of the 68000, its associated memory, and two half height 8"
disks, which replaced the 1 8" disk in the model II. The case colour and 
keyboard colour changed as well.  There were some internal part #
changes over the years, but otherwise, the two use all the
same parts.

As the Model II started to get dated (badly) and folks wanted 
the twin drives of the model 16, but not the 68K, AND Tandy realized
it could save money by reducing the 5 boards (CPU, memory, Floppy contrlr,
video, backplane) in a model II to two, eliminating the backplane
(CPU w mem & FDC, and same old video card) they did it, creating 
the model 12. The upgrade path was then to put in a backplane, cardcage,
and 68K CPU to turn it into a model 16B. The z80CPU was unchanged 
from II->12->16->6000, being 4Mhz all along. In fact the CPU for the
12,16B,6000 is the same part #, and schematically, it resembles the pages
for a model II CPU, FDC, and memory all glued together. Not exactly
mind you, but really close. All the 68K based systems used the z80 as an
I/O processor.

There were 4 68K based CPUs which could be used to upgrade a II/12 to 
68000 system (16/16B/6000), the original (long board) wich came in the 16,
the first generation short board (still 6Mhz),  which came in the late 16's, 
and all the 16B's, the fast short board (8Mhz) which appeared in the 
6000, and the MMU CPU, which was 8Mhz, and supported > 1Meg of 68Kram.


There were 2 68K memory boards, one for 64K drams, one for 256K's which came
out with the 6000.
The first OS for the 16 was TRSDOS16, which was trsdos II with support for
double sided floppies and a loader for 68000 programs. There was a COBOL
OS for running a bunch of COBOL apps, and XENIX, which started with XENIX 1.0,
a UNIX v.7 variant, which migrated to XENIX 3.x, a System III derivitive.

You may sometimes hear about legendary 'Mux Box Systems', with some 
reverence...Tandy had a multiplexor (you don't want to know any more)
which shared the same backplane design with the model II/12/16/6000, but 
rather than 8 slots was 16 slots, and included a number of 4 port 
serial cards. Some folks inside and outside of Tandy realized that 
they could build systems using these pieces, allowing more expansion
than previously (we were running out of slots) allowed. I know of
about half a dozen of these kicking around the country.
-- 
Bob Bownes, aka iii - "Fork twice to avoid zombies"
Warning: This may contain opinions. They belong to me, not to Aule-Tek, 
Sun Microsystems, General Electric or anyone else. But you can rent them.