[Coco] An 8-Slot Multi-Pak Design for my Color Computer Friends

[jdaggett at gate.net]

No problem

I made suggestions that I thought you might consider. 

Layout is an art more so than just a science. While there is science involved, thae art portion 
is gained from years of experience. Knowing what works and what does not comes from 
doing more than learning. 

james



On 5 Jul 2010 at 15:11, Little John (GIMEchip.com) wrote:

> James,
> I was just reading some of my replies to you - As it is impossible to 
> transfer tones of voice, etc. via e-mail, I was afraid that my replies (at 
> least one of them)  to you might have sounded as if I was trying to be 
> rude - This is NOT the case - I just wanted you to know that I value each 
> and every one of your observations regarding this design and you have 
> pointed out plenty of areas that I need to improve - I APPRECIATE THIS my 
> Friend. Thank You - John
> ----- Original Message ----- 
> From: <jdaggett at gate.net>
> To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
> Sent: Monday, July 05, 2010 1:46 PM
> Subject: Re: [Coco] An 8-Slot Multi-Pak Design for my Color Computer Friends
> 
> 
> > On 5 Jul 2010 at 16:06, afra at aurigae.demon.co.uk wrote:
> >
> >> Quoting "Little John (GIMEchip.com)" <sales at gimechip.com>:
> >>
> >> > Had to have a fourth of July Holiday, so now I'm back. Let's have a 
> >> > look see:
> >> >>
> >> >> A huge mistake in not buffering the data bus on the main board. If
> >> >> you are running a stock
> >> >> Coco3, you do run the risk of damaging the MC6809E and the HD6309E
> >> >> if the board
> >> >> becomes detached while powered up.
> >> >>
> >> > That's easy enough to fix. However, even with the databuffer on the
> >> > main board, detaching while powered up could cause damage,
> >> > especially if it were knocked sideways - zap.
> >>
> >> I keep hearing this over and over again, but have not found the 6809E
> >> any more suceptable to damage in this way compared to say a 6502 or a
> >> Z80, and believe me I've done enough (un)intentional
> >> plugging/unplugging things with the power on :( :( I don't recall
> >> killing a 6809 yet.....perhaps I have been lucky.
> >>
> >> Mind this is in a CoCo 1/2 or a Dragon 32/64, so it may be different
> >> in the CoCo 3.
> >>
> >> Cheers.
> >>
> >> Phill.
> >>
> >
> > A lot depends on the load that is being plugged in or unpluged. NMOS 
> > depletion loads are ot
> > designed for hot swapping. So are CMOS outputs. When at a logic one 
> > output, all the current
> > is passing through a NMOS diode that has rather small geometry. Geometry 
> > determines the
> > amount of current that can pass throug the diode. Drawing much more than o 
> > TTL load (~2.4
> > mA) is potentially dangerous. Once that diode load burns out, the port 
> > will no longer function
> > properly. In any case you have been lucky.
> >
> > I went back and rechecked the Coco3 schematic and the databus is buffered 
> > with a LS245.
> > So that concern is not as critical. The address bus is not. It is pulled 
> > high through some
> > resistors that the COco1/2 fail to use. This does help some in transients. 
> > The resistors along
> > with the internal NMOS depletion load act like a current divider. Thus 
> > enough of the
> > damaging current could pass throough the resistors instead of the IC. 
> > Transients can cause
> > latent defects that build up over time to induce a permanent failure.
> >
> > james
> >
> >
> >
> >
> >
> >
> >
> > --
> > Coco mailing list
> > Coco at maltedmedia.com
> > http://five.pairlist.net/mailman/listinfo/coco
> 
> 
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> 
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