P89LPC92X1 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.
Product data sheet Rev. 2.1 — 27 August 2012 42 of 75
NXP Semiconductors
P89LPC9201/9211/922A1/9241/9251
8-bit microcontroller with 8-bit ADC
If a comparator interrupt is enabled (except in Total Power-down mode), a change of the
comparator output state will generate an interrupt and wake-up the processor. If the
comparator output to a pin is enabled, the pin should be configured in the push-pull mode
in order to obtain fast switching times while in Power-down mode. The reason is that with
the oscillator stopped, the temporary strong pull-up that normally occurs during switching
on a quasi-bidirectional port pin does not take place.
Comparators consume power in Power-down and Idle modes, as well as in the normal
operating mode. This fact should be taken into account when system power consumption
is an issue. To minimize power consumption, the user can disable the comparators via
PCONA.5, or put the device in Total Power-down mode.
7.25 KBI
The Keypad Interrupt function (KBI) is intended primarily to allow a single interrupt to be
generated when Port 0 is equal to or not equal to a certain pattern. This function can be
used for bus address recognition or keypad recognition. The user can configure the port
via SFRs for different tasks.
The Keypad Interrupt Mask Register (KBMASK) is used to define which input pins
connected to Port 0 can trigger the interrupt. The Keypad Pattern Register (KBPATN) is
used to define a pattern that is compared to the value of Port 0. The Keypad Interrupt Flag
(KBIF) in the Keypad Interrupt Control Register (KBCON) is set when the condition is
matched while the Keypad Interrupt function is active. An interrupt will be generated if
enabled. The PATN_SEL bit in the Keypad Interrupt Control Register (KBCON) is used to
define equal or not-equal for the comparison.
In order to use the Keypad Interrupt as an original KBI function like in P87LPC76x series,
the user needs to set KBPATN = 0FFH and PATN_SEL = 1 (not equal), then any key
connected to Port 0 which is enabled by the KBMASK register will cause the hardware to
set KBIF and generate an interrupt if it has been enabled. The interrupt may be used to
wake-up the CPU from Idle or Power-down modes. This feature is particularly useful in
handheld, battery-powered systems that need to carefully manage power consumption
yet also need to be convenient to use.
In order to set the flag and cause an interrupt, the pattern on Port 0 must be held longer
than six CCLKs.
7.26 Watchdog timer
The watchdog timer causes a system reset when it underflows as a result of a failure to
feed the timer prior to the timer reaching its terminal count. It consists of a programmable
12-bit prescaler, and an 8-bit down counter. The down counter is decremented by a tap
taken from the prescaler. The clock source for the prescaler can be the PCLK, the nominal
400 kHz watchdog oscillator or low speed crystal oscillator. The watchdog timer can only
be reset by a power-on reset. When the watchdog feature is disabled, it can be used as
an interval timer and may generate an interrupt. Figure 14
shows the watchdog timer in
Watchdog mode. Feeding the watchdog requires a two-byte sequence. If PCLK is
selected as the watchdog clock and the CPU is powered down, the watchdog is disabled.
The watchdog timer has a time-out period that ranges from a few s to a few seconds.
Please refer to the P89LPC9201/9211/922A1/9241/9251 User manual for more details.