[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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