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Old 01-28-2008, 07:35 PM
Grant Stockly Grant Stockly is offline
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Join Date: Jan 2005
Posts: 447
Default Mini680 Altair 680 Memory Expansion Board

As a "promotion" to the Altair 680 buyers I promised a 32k RAM upgrade. Due to the wait they have had to endure, I've decided to add 512k of Flash memory.
  • The memory is available from 0x0000 to 0x7FFF.
  • There is a 2k gap from 0x8000 to 0x87FF to allow for the onboard 1k of memory AND the optional vintage 2k RAM upgrade.
  • The flash memory is available from 0x8800 to 0xC7FF. This is a 16k window.
  • There is a page register (IC U6) at 0xC8FF to select which of the 32 16k pages you want to access.
What does this mean to non-programmers? It means a bone stock Altair with the upgrade will have 33,792 bytes of RAM instead the stock 1024 bytes.

It also means you will be able to boot Basic and the Assembler/Editor without loading a paper tape image. There is also MORE than enough space in 512k for any other data.

So far the only software I have is the Assembler/Editor and two versions of Basic. These won't even use up the first 16k of Flash.

When I tried to assemble these boards, I noticed DigiKey sent me 25 $5 ADC chips instead of 25 $.60 74ALS574s. I am ordering 25 of the correct chip to be shipped FedEx overnight so that I can move forward with getting your kits out the door!

The PCB design, PLD logic code, schematics, etc will all be available for anyone to modify. The PLD is socketed for easy reprogramming.

Here are some pictures, sorry...I don't have one with it installed...

The configuration below shows the required parts for only the 32k memory expansio. The only parts required for flash is the flash itself and the page register.


The upgrade card plugs into the processor socket on the PCB, and the processor plugs into the PCB.


This is what I had to do to make sure the PCB design worked!
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