[Coco] Jingo - Jango - Mars

[Gene Heskett]

On Thursday 15 January 2004 14:35, Roger Taylor wrote:
>At 11:51 AM 1/15/2004 -0500, you wrote:
>>Now theres a thought.  I've been told that for a while at least,
>> the shuttle computers were 6809 machines running os9.  Can anyone
>> confirm/deny that?
>
>Oh, "GIME" a break.
>
>That stemmed probably from a short comment somewhere about some form
> of OS-9 being used somewhere on the shuttle, and I have never even
> found proof in any of it.  The shuttle is loaded with high-speed
> computer equipment, and I highly doubt are beloved 6809 plays any
> major response-intensive role.  If OS-9 ran the coffeemaker, I
> would be totally surprised.
>
>Ofcourse, there's a sad joke in all of this... maybe the reason 2 of
> our shuttles blew up is because they had the IRQs hard-wired like a
> lot of OS-9/MPI users did.  Maybe someone who had done that hack
> before had crippled the shuttle's OS-9 by running a wire directly
> into the CPU's IRQ line?  I dunno.  :)

It doesn't need a wire into the coco, and never did Roger.  What you 
need to do is just run a bus wire in the MPI, any model, that 
connects all 4 sockets together at pin 8.  IRQ steering all bypassed, 
no problem.  But to be nice to the poor cart thats trying to pull 
about 6 of those pullup resistors down, do them a favor and remove at 
least 3 of the pin 8 pullup resistors, along the front edge of the 
mpi board.  There's enough pullups on that IRQ line then that when an 
IRQ goes down, it actually makes a very faint flicker in the video on 
my machine, which is all running on one old PC psu, no line cords 
exist on mine.  Just a jumper out the hole that plugs into a disk 
drive power connector on that psu.

The reason I stress that pullup removal is because there are enough 
pullups on the line that a transistor turning on to pull it down must 
sink (in some versions of the mpi) almost 100 milliamps!  5 to 10 ma 
of pullup is a great plenty.  Some output bugs in some chips aren't 
capable of that >50ma sink over the long haul.

>----------
>Roger Taylor

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty: soap,
ballot, jury, and ammo. Please use in that order."
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by Gene Heskett are:
Copyright 2004 by Maurice Eugene Heskett, all rights reserved.