Thanks to sarnau (Markus F.)  we have a reverse engineered STBook/Stylus test cart. 

However because the 120 pin expansion connector not being available the design is not fully finished. Using his schematic I redesigned the cart and made my own version as a cartridge option.

I also designed a 3D printed case, that supports the board and keeping it in level with the expansion port. 

Link to sarnaus' original project.

https://github.com/sarnau/Atari-STBook-STylus-Test-Cartridge/tree/master

This STBook in the video has a TOS chip with CRC error and the cart detects it correctly. However the initial 00 - 08 error is a glitch in the system. It doesn't matter too much, it can be advanced with the Function button.

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