Advanced Parallel I/O - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 357

Start

Perform reset initialization

Perform key-wake-up initialization

Enable key-wake-up interrupt

Start a timer

Yes

User service request? Service the request

No

No

Timer times out?

Yes

Enter low-power mode
(execute stop or wai instruction)

Yes

after servicing the interrupt

Key-wake-up interrupt?

No I mplemented

in hardware

Stay in low-power mode

Figure 7.43 ■ Logic flow of embedded applications that incorporate key-wake-up feature

Example 7.10
▼

Write an instruction sequence to configure the Port P upper four pins for the key-wake-up
feature. Program Port P so that pins PP7,PP4 generate an interrupt whenever there is a falling
edge applied to any one of these four pins.
Solution:
#include

“c:\miniide\hcs12.inc”

…

bclr DDRP,$F0 ; configure PP<7:4> pins for input

bset PERP,$F0 ; enable PP7 , PP4 pins' pull device