* SIO reigster 3 (CIO Address Selection) bit definitions:
* bit 7 CIO index and data registers enabled
* bit 1-0 CIO indirect registers port address select
* SIO reigster 3 (CIO Address Selection) bit definitions:
* bit 7 CIO index and data registers enabled
* bit 1-0 CIO indirect registers port address select
* 1 index = 0xE2 data = 0xE3
* 2 index = 0xE4 data = 0xE5
* 3 index = 0xEA data = 0xEB
* 1 index = 0xE2 data = 0xE3
* 2 index = 0xE4 data = 0xE5
* 3 index = 0xEA data = 0xEB