An exploration of the Tandy Color Computer 3, and how it allowed a CPU that could only address 64K of RAM, actually access megabytes of physical RAM. We discuss the GIME's MMU, how to program it, sample code to write to 2 megs of physical RAM, and trace through it in MAME's debugger.
Download the code shown in this video: https://cocotownretro.wordpress.com/2025/03/03/how-did-they-do-virtual-memory-in-the-80s/
Previous video on how the CoCo 2 accesses 64K of RAM: https://www.youtube.com/watch?v=PQSmJVuza4U
For more information:
"Understanding and Using the MMU" by Allen C. Huffman
https://www.cocopedia.com/wiki/index.php/Understanding_and_Using_the_MMU
NitrOS-9 EOU Level 2 Technical Reference Manual v0.21 (L. Curtis Boyle)
https://colorcomputerarchive.com/repo/Documents/Manuals/Operating%20Systems/NitrOS-9%20EOU%20Level%202%20Technical%20Reference%20Manual%20v0.21%20%28L.%20Curtis%20Boyle%29.pdf
Inside OS-9 Level II (1987)(Kevin Darling)
https://colorcomputerarchive.com/repo/Documents/Books/Inside%20OS-9%20Level%20II%20%281987%29%28Kevin%20Darling%29.pdf
Assembly Language Programming for the CoCo3 (1987) (Laurence A Tepolt)
https://colorcomputerarchive.com/repo/Documents/Books/Assembly%20Language%20Programming%20for%20the%20CoCo3%20%281987%29%20%28Laurence%20A%20Tepolt%29.pdf
Super Extended BASIC Unravelled II
https://colorcomputerarchive.com/repo/Documents/Books/Unravelled%20Series/super-extended-basic-unravelled.pdf
00:00 Intro
01:49 How to control the MMU
08:43 Sample code to write to 2 Megs
13:02 MAME: View more than just logical memory
15:37 Start stepping