Zorro Bus Termination...

chiark

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So, I'm trying to use both a picasso II and a Buddha on my 1000 on a simple device (BC-520CV) that plugs into an 86 pin connector and gives 3 Zorro II slots.

The devices are recognised in the early startup menu, which is nice :D . The buddha works on its own, which is nice.

When the picasso is bought into the mix, the machine is temperamental. Sometimes it'll boot and then hang when Picasso drivers are loaded, and sometimes it'll start giving spurious read errors from the buddha.

My thoughts are that I'm doing something that the 1000 was never really designed to do, but also that the bus isn't properly terminated.

There's quite a few threads on usenet around this form the early 90s, and bus termination seems to recommend a pull up resistor to +5v through 4k7ohm, and a connection to ground through 1k resistor and a 1000pF capacitor.

Looking at the B2000 schematics, all the lines are terminated with the resistor and cap to ground, but not pulled up to +5.

It strikes me as odd that the +5v connection is needed.

Anyone ever built a zorro terminator, and anyone got any advice?

Code:
                             4.7K 
         Signal<----*--------/\/\/\/\/\-------------->5V+ 
                    | 
                    |                    [B]1000[/B] pf. 
                    |          1.0K 
                    |                      | | 
                    *--------/\/\/\/\/\----| |------->Ground 
                                           | | 
 
                                     *NOTE: must be ceramic

And the thread... http://groups.google.com/group/comp...q=amiga+1000+bus+termination#6211fe1eabbb5c1e
 

chiark

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Well, I dropped Dave Haynie a mail last night and got a reply waiting for me this morning - what a guy!

Quote:
Originally Posted by Dave Haynie
There have been a couple of approaches. And it's not just on the control
signals, but at least on my designs, I had termination on the address
and data buses as well.

On the A2000... damn, it's been awhile... something like a 1K resistor
to a 220pF or 300pF capacitor to ground. The original "Zorro" expansion
board (the original bus design done at Amiga in California) used a 220
pullup/330 pulldown ("Thevenin termination".. same idea as orginally used
on SCSI) on nearly every bus signal -- not the interrupts, of course. I
tried that, but on the 2-layer A2000, I got too much crosstalk, driving
that kind of current.


So first off I'll try the Haynie
wink.gif
termination on all lines. Shouldn't take long to make that.

As an aside, it's great that there's such an obvious enthusiasm from Dave to carry on thinking and corresponding about these things, even though we're now a generation (biological, not technical) away from them... 25 years!
 

Tajmaster

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WOW! This is amazing! Its well cool that Dave is good enough to respond and take an interest in helping an Amiga user in 2010 :) Some of the people in the office here were surprised that one of the original Commodore guys was even aware that there is a small group of enthusiasts around like us :)

Dave, you are ace mate! (y)(y)(y)(y)(y)(y)(y)(y)(y)(y)(y)(y)(y)

And nice one Nick!(y)(y)
 

desiv

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As an aside, it's great that there's such an obvious enthusiasm from Dave to carry on thinking and corresponding about these things, even though we're now a generation (biological, not technical) away from them... 25 years!

That sounded like it was from memory for him!!!

WOW!!

I mean, if someone today asked me, "You know that Free And Reduced Meal tracking program you wrote? Did you store the data as truly relational or did you go more flat file or some other mix?" I'd say..

"ummm... yeah... well.. you see... er..."

And he didn't even design/work on (much?) the A1000!!!

That's incredible.. :eek: :wooha:

desiv

p.s. Yes, that was a real program I wrote and I did intentionally name that program FARM Track.. I thought it was funny at the time.. :wooha: :whistle:
And yes, there's a reason I'm a SysAdmin and not a developer now.
 

chiark

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Yep, I'm guessing it was from memory. But then again, if you've lived with debugging why the bus was failing due to crosstalk, which I guess isn't a particularly easy thing to find, it's going to stick in your memory if it was a nasty thing!
 
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