W77C32_07 Datasheet, PDF (47/78 Pages) Winbond – 8-BIT MICROCONTROLLER

W77C32/W77C032A
11. INTERRUPTS
The W77C032 has a two priority level interrupt structure with 12 interrupt sources. Each of the
interrupt sources has an individual priority bit, flag, interrupt vector and enable bit. In addition, the
interrupts can be globally enabled or disabled.
11.1 Interrupt Sources
The External Interrupts INT0 and INT1 can be either edge triggered or level triggered, depending on
bits IT0 and IT1. The bits IE0 and IE1 in the TCON register are the flags which are checked to
generate the interrupt. In the edge triggered mode, the INTx inputs are sampled in every machine
cycle. If the sample is high in one cycle and low in the next, then a high to low transition is detected
and the interrupts request flag Iex in TCON or EXIF is set. The flag bit requests the interrupt. Since the
external interrupts are sampled every machine cycle, they have to be held high or low for at least one
complete machine cycle. The Iex flag is automatically cleared when the service routine is called. If the
level triggered mode is selected, then the requesting source has to hold the pin low till the interrupt is
serviced. The Iex flag will not be cleared by the hardware on entering the service routine. If the
interrupt continues to be held low even after the service routine is completed, then the processor may
acknowledge another interrupt request from the same source. Note that the external interrupts INT2 to
INT5 are edge triggered only. By default, the individual interrupt flag corresponding to external
interrupt 2 to 5 must be cleared manually by software. It can be configured with hardware cleared by
setting the corresponding bit HCx in the T2MOD register. For instance, if HC2 is set hardware will
clear IE2 flag after program enters the interrupt 2 service routine.
The Timer 0 and 1 Interrupts are generated by the TF0 and TF1 flags. These flags are set by the
overflow in the Timer 0 and Timer 1. The TF0 and TF1 flags are automatically cleared by the
hardware when the timer interrupt is serviced. The Timer 2 interrupt is generated by a logical OR of
the TF2 and the EXF2 flags. These flags are set by overflow or capture/reload events in the timer 2
operation. The hardware does not clear these flags when a timer 2 interrupt is executed. Software has
to resolve the cause of the interrupt between TF2 and EXF2 and clear the appropriate flag.
The Watchdog timer can be used as a system monitor or a simple timer. In either case, when the
time-out count is reached, the Watchdog timer interrupt flag WDIF (WDCON.3) is set. If the interrupt is
enabled by the enable bit EIE.4, then an interrupt will occur.
The Serial block can generate interrupts on reception or transmission. There are two interrupt sources
from the Serial block, which are obtained by the RI and TI bits in the SCON SFR and RI_1 and TI_1 in
the SCON1 SFR. These bits are not automatically cleared by the hardware, and the user will have to
clear these bits using software.
All the bits that generate interrupts can be set or reset by hardware, and thereby software initiated
interrupts can be generated. Each of the individual interrupts can be enabled or disabled by setting or
clearing a bit in the IE SFR. IE also has a global enable/disable bit EA, which can be cleared to
disable all the interrupts, at once.
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Publication Release Date: February 1, 2007
Revision A8