Freescale Semiconductor MC68HC08KH12 User Manual

Advance Information

MC68HC(7)08KH12

 — 

Rev. 1.1

230

Freescale Semiconductor

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Return of all enabled keyboard interrupt pins to logic 1 — As long 
as any enabled keyboard interrupt pin is at logic 0, the keyboard 
interrupt remains set.

The vector fetch or software clear and the return of all enabled keyboard 
interrupt pins to logic 1 may occur in any order.

If the MODEE bit is clear, the keyboard interrupt pin is 
falling-edge-sensitive only. With MODEE clear, a vector fetch or 
software clear immediately clears the keyboard interrupt request.

Reset clears the keyboard interrupt request and the MODEE bit, clearing 
the interrupt request even if a keyboard interrupt pin stays at logic 0.

The keyboard flag bit (KEYEF) in the keyboard status and control 
register can be used to see if a pending interrupt exists. The KEYEF bit 
is not affected by the keyboard interrupt mask bit (IMASKE) which 
makes it useful in applications where polling is preferred.

To determine the logic level on a keyboard interrupt pin, disable the 
pull-up device, use the data direction register to configure the pin as an 
input and then read the data register. 

When a keyboard interrupt pin is enabled, it takes time for the internal 
pullup to reach a logic 1. Therefore a false interrupt can occur as soon 
as the pin is enabled.

To prevent a false interrupt on keyboard initialization:

1. Mask keyboard interrupts by setting the IMASKE bit in the 

keyboard status and control register.

2. Write to DDREx bits to make port pin an input pin.

3. Enable the KBI pins by setting the appropriate KBEIEx bits in the 

keyboard interrupt enable register.