TwoMegCoCo - an SRAM-based 2048kB RAM Expansion for the TANDY Color Computer 3

A TTL logic, SRAM-based 2048kB (2MB) memory expansion for the Color Computer 3. Upper bank registers are write-only, like the older Disto units. All parts are through hole for easy hobbyist assembly.

Motivation

After acquiring a used Disto 2MB memory expansion, I wondered if a similar 1980's TTL-based solution could have been created using SRAM (ignoring the fact that 2MB of SRAM was extremely expensive at the time compared to DRAM), and I wanted to see if I could design a unit using only off-the-shelf TTL circuitry. (And, since, at time of writing this, the MMU extension PCB is still being debugged, the question is yet unanswered :-)).

Obviously, as with the HalfMegCoco project, there is little economic incentive in this project, as the contemporary commercial solutions offer more functionality at a cheaper price. But, there's always some value in building a unit oneself, or at least understanding how the MMU process works by inspecting the actual TTL logic.

Status

Currently, the SRAM board has been confirmed to work with various MMU extension solutions (Boysontech/Cloud9), but I am still designing and debugging the MMU board (would appreciate help, if there is interest).

License

Copyright (C) 2020 RETRO Innovations

These files are free designs; you can redistribute them and/or modify them under the terms of the Creative Commons Attribution-ShareAlike 4.0 International License.

You should have received a copy of the license along with this work. If not, see http://creativecommons.org/licenses/by-sa/4.0/.

These files are distributed in the hope that they will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the license for more details.