From: joe@user.com
"Clu" wrote in message
news:j70d54$ov2$5@speranza.aioe.org...
> On 9/7/11 1:35 AM, kyle york wrote:
>
>>>> I'm finally parting with my TRS-80 Model I. I've all of the parts
>>>> (expansion interface, two floppy drives, power supplies). Boots fine,
>>>> but for some reason doesn't recognize the EI.
>
> Nice! Haven't seen a TRS-80 Model 1 since... grade school? :)
>
> So what was the difference between the 1 and 2 again? I felt like 1-4
> were fairly similar right?
>
>
> . _ . Doctor Clu (of...)
> /{_}{} =PRISON BOARD BBS=
> /(- _O) 972-329-0781
> ( \____ ) telnet://rdfig.net
The Model II was structurally different. It was a 'business' machine, not
personal, and designed to go up against stuff like the ADD 10 that Tandy
actually sold. The Model II kicked it's ass for about 40% of the cost.
It was RAM only. For a full 64K. And the top 32K was 'paged'. There was
a small boot rom that was read only that overlayed 2K of RAM. The system
could be running from the boot rom and still write to the ram at the same
location. Because it was 'all RAM', it could run generic versions of CP/M
and other operating systems once the I/O was written for it.
The Model II was a full 4Mhz from the start.
The Model II used 8" double density disk that were single sided. The 8"
rotational speed coupled with the MFM encoding required that the disk have
DMA transfers to keep up. That meant the Model II 1st track on the disk was
single density and not double density.
The Model II had an enhanced video with a Motorola 6845 CRT controller.
This allowed for programable parameters. Early machines could be destroyed
by this under certain conditions. On the plus side, the screen was crisp
and clear, and could easily be reprogrammed for a 25th line that displayed
the keyboard buffer for programmers with a widely distributed utility. If I
remember right, other neat utilities were OOPS to bring back a previous
command as if you typed it and AG which let you move to any spot on the
screen and execute it as a command instead of typing it.
The keyboard was a serial keyboard, not a memory mapped array.
The machine was structured around the Z80 Mode 2 vectored interrupts with an
enable/disable line down the bus. The CPU had a 'fast adder look ahead'
circuit for handling slow devices down the enable chain. It was important
that there be no empty slots in the motherboard between the CPU card and the
furthest card 'down stream' that used mode 2 interrupts. Cards that didn'
use mode 2 interrupts could be anyways, but if they were placed 'in the
stream' common convention was they would 'pass through' the signals.
The machine was made with separate cards in an 8-slot 80-pin motherboard,
which at least one computer magazine said was the quietest and best designed
bus since the S-100.
Options could be just 'plugged in'. There were multi-com cards, graphic
cards (the Tandy card was an XOR of every pixel on the screen, others were a
TI sprite card for color graphics, and the T2000 video was actually
prototyped on a Model II), other CPU cards (Tandy eventually released a
68000 card, but there was also an 8086 card), network, fixed disk, clock,
control, and others. Tandy published a Model II Tech Ref manual that let
almost anyone design cards for the machine. There were prototype cards
available for it as well, but they were not marketed by Tandy. In addition,
Tandy had a bound copy of the 'Tech Tips' that could be purchased.
Originally these were the top secret internal 'fixes' for any of the Tandy
machines, but in later years were actually sold and were an INCREDIBLE
reference to have on the shelf.
I'm feeling that I'm missing something, but that should do for now.
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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