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techknight

Designing a portable RAM card

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I decided to spin this off from my other thread. There seems to be some interest in this, so i decided to move on with the project. 

 

Here is my progress so far: 

 

post-366-0-80980200-1412452225_thumb.png

 

Still alot to go, but so far so good. Got the busses done, just need to get all the signal/enable/CPLD lines ran. 

 

Turns out the apple guide to the family hardware is the correct one. the developer note is incorrect in pin numbering on the socket but the number to signal table figure appears right, and the designing cards and drivers for macintosh is completely wrong. pins and all. 

Edited by techknight

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Yea, i bet that caused some havok for RAM card makers back in the day. lol. 

 

Anyway, more progress. Pretty much complete to operate as stock. 

 

Just have to add a couple jumpers, extra connection points for the DTACK and /AS line for full 9MB extended addressing. Then of course i need to add the decoupling caps, and route the board. 

 

post-366-0-22959100-1412463831_thumb.png

Edited by techknight

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both. In theory, it should be universal. 

 

the difference between the two models, the Backlit has a Refresh line, whilst the original does not. And the backlit /AS becomes /RAMCS, meaning its stuck at a 5MB ceiling, which is why I will have a pin to allow a wire to branch off to the next slot to pick up /AS for the full 9MB. 

 

I will also have a DTACK pin as well, that will connect to the CPU DTACK line to allow the remaining 4MB of address space to be mapped to RAM without throwing bus errors. 

 

In a nutshell, if you want all 9MB, you will have 2 plug-in wires coming of the board going to the ROM slot. or maybe PDS. If you dont want wires, your stuck at 5MB. 

Edited by techknight

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No thoughts? hmm... Guess its a monologue

 

Anyway, board routing time!

You're doing great. We'll jump in if you screw up. :)

 

Plus, I don't access the internet much on the weekends, when you're likely to be making progress on this.

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All done. ground planes are routed, VIA stitching is done, and then the JTAG header installed. Along with some diagnostic LEDs. 

 

Now is finding a PCB service that can run that board, the traces and vias are kinda tight. 

 

post-366-0-70799800-1412813343_thumb.png

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