W77LE532_07 Datasheet, PDF (47/88 Pages) Winbond – 8-BIT MICROCONTROLLER

W77LE532/W77L532A
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
Table 8. Vector locations for interrupt sources
SOURCE
VECTOR ADDRESS
Timer 0 Overflow
000Bh
Timer 1 Overflow
001Bh
Timer 2 Interrupt
002Bh
External Interrupt 2
0043h
External Interrupt 4
0053h
Watchdog Timer
0063h
SOURCE
External Interrupt 0
External Interrupt 1
Serial Port
Serial Port 1
External Interrupt 3
External Interrupt 5
VECTOR ADDRESS
0003h
0013h
0023h
003Bh
004Bh
005Bh
The vector table is not evenly spaced; this is to accommodate future expansions to the device family.
Execution continues from the vectored address till an RETI instruction is executed. On execution of
the RETI instruction the processor pops the Stack and loads the PC with the contents at the top of the
stack. The user must take care that the status of the stack is restored to what is was after the
hardware LCALL, if the execution is to return to the interrupted program. The processor does not
notice anything if the stack contents are modified and will proceed with execution from the address put
back into PC. Note that a RET instruction would perform exactly the same process as a RETI
instruction, but it would not inform the Interrupt Controller that the interrupt service routine is
completed, and would leave the controller still thinking that the service routine is underway.
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Publication Release Date: February 1, 2007
Revision A7