MC68HC908RF2 Datasheet, PDF (189/254 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Keyboard/External Interrupt Module (KBI)
Functional Description
14.4.3 KBI Module During Break Interrupts
The system integration module (SIM) controls whether the IRQ1 or
keyboard interrupt latches can be cleared during the break state. The
BCFE bit in the break flag control register (BFCR) enables software to
clear the latches during the break state. (See 6.8.3 SIM Break Flag
Control Register.)
To allow software to clear the IRQ1 or keyboard latches during a break
interrupt, write a logic 1 to the BCFE bit. If a latch is cleared during the
break state, it remains cleared when the MCU exits the break state.
To protect the latch during the break state, write a logic 0 to the BCFE
bit. With BCFE at logic 0 (its default state), writing to the ACKI or ACKK
bits in the IRQ and keyboard status and control register during the break
state has no effect on the IRQ1 or keyboard latches.
14.4.4 Keyboard Interrupt Pins
Writing to the KBIE6–KBIE1 bits in the keyboard interrupt enable register
independently enables or disables each port A 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 an IRQ1/keyboard interrupt request.
An IRQ1/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.
MC68HC908RF2
MOTOROLA
Keyboard/External Interrupt Module (KBI)
Advance Information
189