W77E532 Datasheet, PDF (47/86 Pages) Winbond – 8 BIT MICROCONTROLLER

W77E532/W77E532A
Table 7. Priority structure of interrupts
SOURCE
External Interrupt 0
Timer 0 Overflow
External Interrupt 1
Timer 1 Overflow
Serial Port
Timer 2 Overflow
Serial Port 1
External Interrupt 2
External Interrupt 3
External Interrupt 4
External Interrupt 5
Watchdog Timer
FLAG
IE0
TF0
IE1
TF1
RI + TI
TF2 + EXF2
RI_1 + TI_1
IE2
IE3
IE4
IE5
WDIF
PRIORITY LEVEL
1(highest)
2
3
4
5
6
7
8
9
10
11
12 (lowest)
The interrupt flags are sampled every machine cycle. In the same machine cycle, the sampled
interrupts are polled and their priority is resolved. If certain conditions are met then the hardware will
execute an internally generated LCALL instruction which will vector the process to the appropriate
interrupt vector address. The conditions for generating the LCALL are
1. An interrupt of equal or higher priority is not currently being serviced.
2. The current polling cycle is the last machine cycle of the instruction currently being executed.
3. The current instruction does not involve a write to IP, IE, EIP or EIE registers and is not a RETI.
If any of these conditions are not met, then the LCALL will not be generated. The polling cycle is
repeated every machine cycle, with the interrupts sampled in the same machine cycle. If an interrupt
flag is active in one cycle but not responded to, and is not active when the above conditions are met,
the denied interrupt will not be serviced. This means that active interrupts are not remembered; every
polling cycle is new.
The processor responds to a valid interrupt by executing an LCALL instruction to the appropriate
service routine. This may or may not clear the flag which caused the interrupt. In case of Timer
interrupts, the TF0 or TF1 flags are cleared by hardware whenever the processor vectors to the
appropriate timer service routine. In case of external interrupt, INT0 and INT1, the flags are cleared
only if they are edge triggered. In case of Serial interrupts, the flags are not cleared by hardware. In the
case of Timer 2 interrupt, the flags are not cleared by hardware. The Watchdog timer interrupt flag
WDIF has to be cleared by software. The hardware LCALL behaves exactly like the software LCALL
instruction. This instruction saves the Program Counter contents onto the Stack, but does not save the
Program Status Word PSW. The PC is reloaded with the vector address of that interrupt which caused
the LCALL. These vector address for the different sources are as follows
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Publication Release Date: June 30, 2009
Revision A10