This is not the original implementation of the Stellation Two daughter-board nor a clone of it.
The original daughter-board made use of one 74S288 prom and 74LS367 Hex Buffer to create a custom memory mapping.
The high cost of 74S288 prom burners and scarce availability of 74S288 proms suggested to implement a different solution.
Then one ATmel ATF16V8C PLD has been programmed to emulate a prom with the right ram memory mapping combination.
A switch has been added to allow for normal/OS9 memory mapping selection.
When installing this daughter-board, chip at location U1 of the 6809 main board (74LS14) must be exchanged with a 74lS04 as recommended in the original Stellation Two OS9 BASIC09 documentation.
633-A12EH A12EH 1 SWITCH SPDT ON NONE ON 28VDC 28VAC
DISCLAIMER
This application (PCB schematic and PROM code) is released under the Creative Commons Attribution-Non Commercial-ShareAlike 4.0 International Public License.
The Author is not responsible for any direct or indirect damage or any kind of consequence, direct or indirect, should arise from the implementation of this project.