This circuit will add 32k of RAM to a 2068 for about $25.00. It can be installed without removing the circuit board from the lower half of the case.
The RAM occupies the upper half of the dock bank from 32768 to 65535. It can be disabled if you have something else that uses this address space in the dock bank.
It will also allow you to SAVE and LOAD on tape, files that reside in the dock bank. This is something that you normally can’t do, as the tape routines are in the EXROM bank and everyone knows you cant mix DOCK chunks and EXROM chunks. Don’t they?
The switch and resistor can be eliminated if you never plan to disable the RAM. The RAM chip is a 64256LP-150 static RAM, the other chip is a 74LS00.
The SRAM chip is piggy-backed onto the EXROM by carefully bending pins 1,20,22,26,27 of the SRAM out and back over the top. Then solder all remaining pins to the EXROM chip or solder a 28 pin lo-profile socket to the EXROM chip.
You should probably remove the EXROM from its socket for the solder operation.
The 74LS00 can be mounted on top of the 74LS157, just to the left of the Exrom.
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