11.5.1 Edge-only sensitivity
Synchronous logic is used to detect edges. A falling edge is detected when an enabled
keyboard interrupt (KBIx_PE[KBIPEn]=1) input signal is seen as a logic 1 (the
deasserted level) during one bus cycle and then a logic 0 (the asserted level) during the
next cycle. A rising edge is detected when the input signal is seen as a logic 0 (the
deasserted level) during one bus cycle and then a logic 1 (the asserted level) during the
next cycle.
Before the first edge is detected, all enabled keyboard interrupt input signals must be at
the deasserted logic levels. After any edge is detected, all enabled keyboard interrupt
input signals must return to the deasserted level before any new edge can be detected.
A valid edge on an enabled KBI pin will set KBIx_SC[KBF]. If KBIx_SC[KBIE] is set,
an interrupt request will be presented to the MPU. Clearing of KBIx_SC[KBF] is
accomplished by writing a 1 to KBIx_SC[KBACK].
11.5.2 Edge and level sensitivity
A valid edge or level on an enabled KBI pin will set KBIx_SC[KBF]. If
KBIx_SC[KBIE] is set, an interrupt request will be presented to the MCU. Clearing of
KBIx_SC[KBF] is accomplished by writing a 1 to KBIx_SC[KBACK], provided all
enabled keyboard inputs are at their deasserted levels. KBIx_SC[KBF] will remain set if
any enabled KBI pin is asserted while attempting to clear KBIx_SC[KBF] by writing a 1
to KBIx_SC[KBACK].
11.5.3 KBI Pullup Resistor
Each KBI pin, if enabled by KBIx_PE, can be configured via the associated I/O port pull
enable register, see Parallel input/output chapter, to use:
• an internal pullup resistor, or
• no resistor
If an internal pullup resistor is enabled for an enabled KBI pin, the associated I/O port
pull select register (see I/O Port chapter) can be used to select an internal pullup resistor.
Functional Description
MC9S08PA4 Reference Manual, Rev. 5, 08/2017
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Summary of Contents for MC9S08PA4
Page 1: ...MC9S08PA4 Reference Manual Supports MC9S08PA4 Document Number MC9S08PA4RM Rev 5 08 2017 ...
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Page 28: ...System clock distribution MC9S08PA4 Reference Manual Rev 5 08 2017 28 NXP Semiconductors ...
Page 150: ...Port data registers MC9S08PA4 Reference Manual Rev 5 08 2017 150 NXP Semiconductors ...
Page 196: ...Human machine interfaces HMI MC9S08PA4 Reference Manual Rev 5 08 2017 196 NXP Semiconductors ...
Page 224: ...Instruction Set Summary MC9S08PA4 Reference Manual Rev 5 08 2017 224 NXP Semiconductors ...
Page 232: ...Functional Description MC9S08PA4 Reference Manual Rev 5 08 2017 232 NXP Semiconductors ...
Page 258: ...FTM Interrupts MC9S08PA4 Reference Manual Rev 5 08 2017 258 NXP Semiconductors ...
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Page 398: ...Resets MC9S08PA4 Reference Manual Rev 5 08 2017 398 NXP Semiconductors ...
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