Version 4 PLD address decoder and 64K Memory Map

A project log for Nanocomp 6809 8 Bit Retro Computer on Breadboards

Wireless World Magazine in January and June 1981 published this design. Reproduced on solderless breadboards using the original Monitor ROM

dave-henryDave Henry 11/13/2022 at 23:110 Comments

The next update to the Nanocomp has been provided on YouTube and GitHub.  

The first video discusses how to ensure reliable breadboard projects by making sure the power distribution to the project is good as possible. Many people reproducing breadboard projects such as those like Ben Eaters have difficult to trace problems with power, normally because voltages on some breadboards drop to below 4 Volts. The recommendations are then applied to the Nanocomp project.

With Version 4 the original design address decoder was replaced with an Atmel ATF22VL10 PLD (GAL) Programable Logic Device. This was first confirmed as working with the Original Memory map. 

The final part shows how the original 32K Memory map of the original 1981 Nanocomp design was updated to use the full 64K address range of the 6809 processor. The Atmel ATF22VL10 PLD was updated for the next 64K memory map and the Monitor ROM updated to run from the top 32K of memory.

GitHub has been updated with the latest KiCad schematic, the PLD configuration files and the revised Monitor assembler source.

The next updates after this will be adding a VGA compatible video controller to the design over a number of iterations.