I've learned that port 6 is the shock port. Previously it was thought to always read 1, but it reads 0 when the reed is in contact. Attached is a test ROM to demonstrate. As implied, 1 = reed not touching, 0 = reed touching

Additionally, on my unit, EEPROM clock reads back as 1 while pokemini shows it as 0.

(This test ROM was initially written to test if the rumble port was 2-way, hence the name. But that has yet to be confirmed/denied.)

io_test.zip