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View Full Version : Memory Merchant and Morrow 64K Static RAM boards.



deramp5113
August 20th, 2015, 04:39 PM
These two 64K static RAM boards are actually the same board and allow mixing of 2K static RAM chips and 2716 EPROMs. This type of board can be very handy to have when working with vintage computers. Unfortunately, they only allow disabling of a single 2K block, so any computer that needs more than a 2K "hole" in RAM (e.g., Sol-20, Vector Graphic systems, etc.) can't use this board.

The 2K block to disable (out of a 16K segment) is selected with a single jumper across two pins of a 2x8 header. You can't jumper more than one 2K block because it ends up shorting the active outputs of a 74LS138 to each other.

To get around this, I made some jumpers that put a Schottky diode across the pins instead of a hard short. This way, you can put from one to eight jumpers on and disable from 2K to 16K as needed. I'm about to order more Schottkys and pin housings so I can build more of these. Anyone need some of these jumpers?

Mike