[Coco] Coco Cartridge Prototyping Pak PCB

[Kip Koon]

Hi Everybody!

The Coco Cartridge Prototyping Pak PCB is designed and ready for
scrutinizing.  I'd like to get a few interested people to examine the
schematic and make sure I have done my homework correctly.

The prototyping PCB provides for two types of address decoding using all DIP
style chips.  

The first type of decoding stays within the $FF40 - $FF5F addressing range
and decodes all the way down to a single byte.  

The Second type of address decoding allows for setting the base address to
any one of 8 blocks of 32 bytes in the $FFxx addressing block.  

There are four sets of jumpers that determines where the chip will be
addressed with only one jumper block/strap needed in any one set of jumpers.


SV1 selects which one of the 8 - 4 byte blocks in the 32 byte block you wish
to use.  

SV2 sets which 1 of 4 bytes of that 4 byte block you wish to use.  

SV3 if used will select which one of the 8 - 32 byte blocks you wish to use
in the $FFxx addressing block.  

SV4 selects which type of addressing you wish - The $FF40 - $FF5F addressing
range or The $FFxx addressing range.

For most experiments, A 1 or 4 byte block is enough.  I just realized though
that if an 8 byte block of addresses are required, then a 2 to 4 decoder
will be needed to decode the A4 and A3 address lines with the output of SV3
connected to the active low gate input of a 74LS139 2 to 4 decoder chip.
There actually is a spare decoder on the PCB already which I could wire up
for this scenario.  

This should satisfy almost every address decoding scenario I can think of.  

Now for you guys to think of the impossible!  :D  When this has been
thoroughly scrutinized for errors, the boards will be available from OSHPark
for about $40 plus shipping unless we use a different PCB Fabrication house
which will require a big order to get the prices down similar to how the
N8VEM group gets there PCBs made.  If it wasn't for OSHPark's $5 per square
inch of board space charge, I'd use OSHPark for big PCB designs too and this
is what I would consider as the beginning of the Bigger PCBs.

I'll be back online after a few hours to find out what everyone thinks of my
design.  Here are links to a rendering of the PCB from OSHPark.  

https://www.dropbox.com/s/yy17jwamkejx94s/Coco%20Cartridge%20Prototyping%20P
ak%20-%20Top.png?dl=0

https://www.dropbox.com/s/euo6vq5ukkr8gvu/Coco%20Cartridge%20Prototyping%20P
ak%20-%20Bottom.png?dl=0

If the links get split up on two different lines, just highlight both lines
and paste it into your browser.  I do it all the time.  The first link is
the top of the PCB and the second link is the Bottom of the PCB.  Any
addressing not needed of course does not need to be populated.  Have fun
folks and Take care my friends.

 

Kip Koon

 <mailto:computerdoc at sc.rr.com> computerdoc at sc.rr.com

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