AT89LP428 Datasheet, PDF (74/149 Pages) ATMEL Corporation – 8-bit Microcontroller with 4K/8K Bytes In-System Programmable Flash

Figure 13-14. Three-Phase Mode with Channel B Disabled
CCA
CCB
CCC
PHSD
PHS = 010B, CCB Disabled
14. External Interrupts
The INT0 (P3.2) and INT1 (P3.3) pins of the AT89LP428/828 may be used as external interrupt
sources. The external interrupts can be programmed to be level-activated or transition-activated
by setting or clearing bit IT1 or IT0 in Register TCON. If ITx = 0, external interrupt x is triggered
by a detected low at the INTx pin. If ITx = 1, external interrupt x is edge-triggered. In this mode if
successive samples of the INTx pin show a high in one cycle and a low in the next cycle, inter-
rupt request flag IEx in TCON is set. Flag bit IEx then requests the interrupt. Since the external
interrupt pins are sampled once each clock cycle, an input high or low should hold for at least 2
oscillator periods to ensure sampling. If the external interrupt is transition-activated, the external
source has to hold the request pin high for at least two clock cycles, and then hold it low for at
least two clock cycles to ensure that the transition is seen so that interrupt request flag IEx will
be set. IEx will be automatically cleared by the CPU when the service routine is called if gener-
ated in edge-triggered mode. If the external interrupt is level-activated, the external source has
to hold the request active until the requested interrupt is actually generated. Then the external
source must deactivate the request before the interrupt service routine is completed, or else
another interrupt will be generated. Both INT0 and INT1 may wake up the device from the
Power-down state.
15. General-purpose Interrupts
The GPI function provides 8 configurable external interrupts on Port 1. Each port pin can detect
high/low levels or positive/negative edges. The GPIEN register select which bits of Port 1 are
enabled to generate an interrupt. The GPMOD and GPLS registers determine the mode for each
individual pin. GPMOD selects between level-sensitive and edge-triggered mode. GPLS selects
between high/low in level mode and positive/negative in edge mode. A block diagram is shown
in Figure 15-1. The pins of Port 1 are sampled every clock cycle. In level-sensitive mode, a valid
level must appear in two successive samples before generating the interrupt. In edge-triggered
mode, a transition will be detected if the value changes from one sample to the next. When an
interrupt condition on a pin is detected, and that pin is enabled, the appropriate flag in the GPIF
register is set. The flags in GPIF must be cleared by software. Any GPI interrupt may wake up
the device from the Power-down state.
74 AT89LP428/828
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