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

[Little John (GIMEchip.com)]

Understood - the things that I have read that you are working on promise to 
be Amazing Feats of Genius :-). -John
----- Original Message ----- 
From: <jdaggett at gate.net>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Monday, July 05, 2010 11:40 AM
Subject: Re: [Coco] An 8-Slot Multi-Pak Design for my Color Computer Friends


> On 5 Jul 2010 at 9:05, Little John (GIMEchip.com) wrote:
>
>> Had to have a fourth of July Holiday, so now I'm back. Let's have a look
>> see:
>>
>> > First
>> >
>> > 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.
>>
>
> Yes that is true. The MC6809 does not like to drive large capacitive 
> loads. The additional
> runner lenghts and connectors add capacitance that degrades noise immunity 
> and potentially
> damaging current transients during witching. Frankly I am not surprised 
> that the original MPI
> has more problems. The duffers should have been on the inside of the Coco 
> and not on the
> MPI side.
>
>
>> > Second
>> >
>> > why the dip switches on the Control and clock lines. A wrong setting on
>> > the dip switches and
>> > you have a nonfunctioning board that can lead to frustration.
>> >
>> If I build it, I'll know what the DIP swicthes do. But again easily 
>> fixed -
>> jumper wires instead of the DIP switches if you don't want the DIP 
>> switches.
>>
>
> True. Still the E clock line should feed directly to the slot connectors 
> from the buffer. No
> jumpers or any switches.
>
>> > Third
>> >
>> > What is the function of Q1?
>> >
>> It is supposed to tell the ATX power supply to switch on when the CoCo
>> Powers on - this was stated in the text. However, this is pretty lame - A
>> reed relay might have been better or just a switch to turn the darned 
>> thing
>> on. Yeah - the switch probably would be best.
>>
>
> Okay that makes sense. Did not realize that you are powering this off an 
> ATX supply.
>
>> > Fourth
>> >
>> > Your ground plane on the top and bottom are basically floating planes 
>> > that
>> > are tied at but just
>> > a few spots. You have all your locic tied to GND1 and then this large
>> > plane on both sides is
>> > GND. You also have fingers that are floating that is bad for noise
>> > immunity. Either use one
>> > ground or tie them in a star pattern and eliminate the floating 
>> > fingers.
>> >
>> > just a few things I see wrong or bothersome.
>>
>> I did use only one ground - the GND/1 is the Library Name for the Ground
>> Symbol that I have chosen - ALL Grounds in the schematic are electrically
>> tied to the GND net name. This can be seen if you load it up in EAGLE and
>> right click to get the properties of any GND connection - they are all 
>> tied
>> to GND.
>>
>
> They are? Why then highlighting the plane states GND and the runner from 
> runner CN2 is
> GND1. That means you have two grounds and they are tied together at some 
> other point on
> the board.
>
> At least I would not do it that way. If they are supposed to be one then 
> make them one. Not
> two and then use some etch someplace on the board to tie them togeter 
> unless you intend to
> do a star connection. If tha twas your intent the star point should be 
> where the board make
> ground connections to the outide world. Not internal to the board.
>
>> If you find any more problems - fire away - it'll help me fix this right 
>> up.
>> I'm just a hobbyist - no formal training, so this design MUST be 
>> SCRUTINIZED
>> thoroughly in order to work out all of the bugs. -John
>>
>
> If i find time to do a more in depth review I may. Right now I have more 
> important things to
> do.
>
> james
>
> --
> Coco mailing list
> Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco


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