MC68HC908AT32 Datasheet, PDF (281/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 24
Keyboard Interrupt Module (KBD)
NOTE
This keyboard module is for the MC68HC08AZ32 emulator only.
24.1 Introduction
The keyboard interrupt module (KBD) provides five independently maskable external interrupt pins.
24.2 Features
KBD features include:
• Five keyboard interrupt pins with separate keyboard interrupt enable bits and one keyboard
interrupt mask
• Hysteresis buffers
• Programmable edge-only or edge- and level- interrupt sensitivity
• Automatic interrupt acknowledge
• Exit from low-power modes
24.3 Functional Description
Writing to the KBIE4–KBIE0 bits in the keyboard interrupt enable register independently enables or
disables each port G or port H pin as a keyboard interrupt pin. Enabling a keyboard interrupt pin also
enables its internal pullup device. A logic 0 applied to an enabled keyboard interrupt pin latches a
keyboard interrupt request.
A keyboard interrupt is latched when one or more keyboard pins goes low after all were high. The MODEK
bit in the keyboard status and control register controls the triggering mode of the keyboard interrupt.
• If the keyboard interrupt is edge-sensitive only, a falling edge on a keyboard pin does not latch an
interrupt request if another keyboard pin is already low. To prevent losing an interrupt request on
one pin because another pin is still low, software can disable the latter pin while it is low.
• If the keyboard interrupt is falling edge- and low level-sensitive, an interrupt request is present as
long as any keyboard pin is low.
MC68HC908AT32 Data Sheet, Rev. 3.1
Freescale Semiconductor
281