p89lpc9351 NXP Semiconductors, p89lpc9351 Datasheet - Page 45

• Manufacturer Part Number: p89lpc9351
• Description: 8-bit Microcontroller With Accelerated Two-clock 80c51 Core 8 Kb 3 V Byte-erasable ?ash With 8-bit Adc
• Manufacturer: NXP Semiconductors

NXP Semiconductors
P89LPC9351_1
Preliminary data sheet
7.27 KBI
7.28 Watchdog timer
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 87LPC76x 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.
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 external 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.
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 P89LPC9351 User manual for more details.
Rev. 01 — 19 November 2008
Figure 19
8-bit microcontroller with 8-bit ADC
shows the watchdog timer in
P89LPC9351
© NXP B.V. 2008. All rights reserved.
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