T11 design WAS - Re: Inside old games machines, was: Re: Simulated CP/M-68K?

Ethan Dicks ethan.dicks at gmail.com
Tue Jun 19 09:33:29 CDT 2007


On 6/19/07, Robert Borsuk <rborsuk at colourfull.com> wrote:
> I've been loosely following this thread and never heard of a T11 from
> DEC.  So good'ole  Google and Bitsavers saves the day, but it get's
> me thinking.  Has anybody done any design's with this processor?

Yes (see the thread where it appears in a few video games).  DEC used
it as a PDP-11-instruction-set-compatible microcontroller.  It appears
on a few peripheral boards (the RQDX3 comes to mind), and a few other
places.

For some real boots-on-the-ground history, we turn to Bob Supnik...

http://simh.trailing-edge.com/semi/t11.html

(I did not know about his T-11-based RT-11 box - I should ask him about it).

> Why wasn't this processor used instead of the 6100?

In what?  In video games?  the 6100 _might_ have been a competetive
architecture when it was new in the mid-to-late 1970s, but as
competition against an early 8-bit micro, not a 16-bit micro, which
the T-11 is.  From looking at the Atari line at the time, it seems
that they were positioning the T-11 against the Motorola 68000.
Presumably there was some engineering or marketing or production
reason to go with the T-11 over the 68000, but, as much as I like the
PDP-11, I can't imagine what that would be.  Perhaps the $10/unit cost
that Bob Supnik cites was favorable compared to, say, trying to go
over 8MHz on a 68000, but that's mere speculation.  I know that at the
low-point in the 68000 timeline, it was going for about $3 each in
reasonable quantities, but I don't know where that curve compares to
the $10 each for the T-11.

I'm not saying you _couldn't_ make a video game based on the IM6100,
but it didn't happen to have been done, and would probably just end up
as a demonstration of engineering prowess, not something that would
have made sense from a business standpoint in 1976.

-ethan



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