Philips Semiconductors
P89LPC920/921/922/9221
8-bit microcontrollers with two-clock 80C51 core
Product data Rev. 08 — 15 December 2004 30 of 46
9397 750 14469
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
8.20.2 Comparator interrupt
Each comparator has an interrupt flag contained in its configuration register. This flag
is set whenever the comparator output changes state. The flag may be polled by
software or may be used to generate an interrupt. The two comparators use one
common interrupt vector. If both comparators enable interrupts, after entering the
interrupt service routine, the user needs to read the flags to determine which
comparator caused the interrupt.
8.20.3 Comparators and power reduction modes
Either or both comparators may remain enabled when Power-down or Idle mode is
activated, but both comparators are disabled automatically in Total Power-down
mode. 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.
8.21 Keypad interrupt (KBI)
The Keypad Interrupt function 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 6 CCLKs.
