Special Registers; I/O Registers; Game Boy Tm Cpu Manual - Nintendo DMG-01 - Game Boy Console Manual

TM
Game Boy CPU Manual
5. High-to-Low of P10-P13
This interrupt occurs on a transition of any of the
keypad input lines from high to low. Due to the fact
that keypad "bounce"* is virtually always present,
software should expect this interrupt to occur one
or more times for every button press and one or more
times for every button release.
* - Bounce tends to be a side effect of any button
making or breaking a connection. During these
periods, it is very common for a small amount of
oscillation between high & low states to take
place.

2.13. Special Registers

2.13.1. I/O Registers

1. FF00 (P1)
Name
Contents - Register for reading joy pad info
Bit 7 - Not used
Bit 6 - Not used
Bit 5 - P15 out port
Bit 4 - P14 out port
Bit 3 - P13 in port
Bit 2 - P12 in port
Bit 1 - P11 in port
Bit 0 - P10 in port
by DP
- P1
and determining system type.
2.12.2. Interrupt Descriptions
(R/W)
Page 35