Tag: mydos

Adds 1 MB of banked RAM to an Atari 1200XL or 800XL with a 30-pin SIMM and custom refresh and bank-selection logic.

The archived article provides the circuit discussion, 1200XL connection table, SIMM pinout, and software notes but describes the 800XL only as having similar connection points. It is an advanced historical wire-and-perfboard build. The author reports that the SpartaDOS cartridge does not function with this configuration and that ordinary SpartaDOS and much commercial software see only a 320XE-style subset; MYDOS 4.5.1M or newer needs the documented page sequence.

Adds a vintage 1 MB banked-memory board to an Atari 800XL or 1200XL with several selectable PIA banking configurations.

Only archived installation instructions and the used market were verified. Installation requires the original Newell board or a faithful equivalent, memory devices, extensive motherboard wiring, isolated IC pins, and model-specific changes; a 1200XL also needs three address-trace changes. The recommended banking method preserves OS control and ANTIC banking but repurposes other PIA bits and may require BASIC and diagnostic switches. The top RF shield may no longer fit.