Pin 26 on the internal serial slot is listed as a “General Purpose I/O”. The Internal Serial Slot Developers Guide says that this pin can be configured as either an input or output.
The question is, how is this pin connected? What GPIO or DIO pin is it connected to?
Well the answer seems to be GPIO #9. Again a little tweaking of Eckhart’s code lets you call the relevant functions and toggle the pin.
Also, you can configure the pin as an input, and things work as expected. From a hardware design perspective, however, this pin will likely be an output (pulled to ground) until your software configures it as an input… so your hardware should be tolerant of the pin as both an input and an output.
One interesting note, is the N2 platform overview (p 1-29) document lists this GPIO as “Serial NOT CP Enable”. This doesn’t seem accurate. Also DIO #2 is listed as “Available for Configuration to the Slot”. DIO #2 is the output we use to configure SerPortSel3. Perhaps there is a documentation error here and these signals are reversed. Maybe these were reversed in the final hardware design and the documents were never updated. Its a mystery.
I also updated my little app to support the GPIO pin for both input and output. I’ll post the code to Github soon. Really this is intended for developer use, so it is not recommended that the average user install this application on their Newton.