Datasheet

MC68HC908QY4•MC68HC908QT4•MC68HC908QY2•MC68HC908QT2•MC68HC908QY1•MC68HC908QT1

180 Keyboard Interrupt Module (KBI) MOTOROLA

Keyboard Interrupt Module (KBI)

NON-DISCLOSURE AGREEMENT REQUIRED

A keyboard interrupt is latched when one or more keyboard interrupt

inputs 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 interrupt input does not latch an interrupt request if

another keyboard pin is already low. To prevent losing an interrupt

request on one input because another input is still low, software

can disable the latter input 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 interrupt input

is low.

If the MODEK bit is set, the keyboard interrupt inputs are both falling

edge and low-level sensitive, and both of the following actions must

occur to clear a keyboard interrupt request:

• Vector fetch or software clear — A vector fetch generates an

interrupt acknowledge signal to clear the interrupt request.

Software may generate the interrupt acknowledge signal by

writing a logic 1 to the ACKK bit in the keyboard status and control

the keyboard interrupt inputs and require software to clear the

keyboard interrupt request. Writing to the ACKK bit prior to leaving

an interrupt service routine can also prevent spurious interrupts

due to noise. Setting ACKK does not affect subsequent transitions

on the keyboard interrupt inputs. A falling edge that occurs after

writing to the ACKK bit latches another interrupt request. If the

keyboard interrupt mask bit, IMASKK, is clear, the central

processor unit (CPU) loads the program counter with the vector

address at locations $FFE0 and $FFE1.

• Return of all enabled keyboard interrupt inputs to logic 1 — As

long as any enabled keyboard interrupt pin is at logic 0, the

keyboard interrupt remains set. The auto wake-up interrupt input,

AWUIREQ, will be cleared only by writing to ACKK bit in KBSCR

or reset.