mc68hc08ln56 Freescale Semiconductor, Inc, mc68hc08ln56 Datasheet - Page 93

• Manufacturer Part Number: mc68hc08ln56
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

9.4 Keyboard Initialization
When a keyboard interrupt pin is enabled, it takes time for the internal pull-up to reach a logic one, so it
is possible that an interrupt could occur when the pin is initially enabled.
To prevent this, it is recommended that the keyboard interrupt be masked with the IMASKK bit in the
KBSCR register before enabling the pin and that the ACKK bit be used to acknowledge the potential false
interrupt before setting IMASKK back to zero. An edge-only type of interrupt can be acknowledged
immediately after enabling the pin. An edge- and level-triggered interrupt must be acknowledged after a
delay which is dependant on the external load.
Another way to avoid a false interrupt is to set the appropriate bit of port A to an output driving a logic one,
before enabling the keyboard input.
9.5 I/O Registers
These registers control and monitor operation of the keyboard module:
9.5.1 Keyboard Status and Control Register (KBSCR)
The keyboard status and control register performs these functions:
Bits 7–4 — Not used
KEYF — Keyboard Flag Bit
ACKK — Keyboard Acknowledge Bit
Freescale Semiconductor
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These read-only bits always read as logic zeros.
This read-only bit is set when a keyboard interrupt is pending. Reset clears the KEYF bit.
Writing a logic one to this read/write bit clears the keyboard interrupt latch. ACKK always reads as logic
zero. Reset clears ACKK.
1 = Keyboard interrupt pending
0 = No keyboard interrupt pending
Keyboard status and control register (KBSCR)
Keyboard interrupt enable register (KBIER)
Flags keyboard interrupt requests
Acknowledges keyboard interrupt requests
Masks keyboard interrupt requests
Controls keyboard latch triggering sensitivity
KBSCR
$001A
Reset:
Read:
Write:
MC68HC08LN56 • MC68HC708LN56 General Release Specification, Rev. 2.1
Figure 9-3. Keyboard Status and Control Register (KBSCR)
Bit 7
0
0
= Unimplemented
6
0
0
5
0
0
4
0
0
KEYF
3
0
ACKK
2
0
0
IMASKK
1
0
Keyboard Initialization
MODEK
Bit 0
0
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