W78E054D Datasheet, PDF (46/89 Pages) List of Unclassifed Manufacturers – 8-bit microcontroller

W78E054D/W78E052D Data Sheet
PRIORITY BITS
IPH
0
0
1
1
IP/
XICON.7/
XICON.3
0
1
0
1
INTERRUPT PRIORITY LEVEL
Level 0 (lowest priority)
Level 1
Level 2
Level 3 (highest priority)
The interrupt flags are sampled every machine cycle. In the same machine cycle, the sampled inter-
rupts are polled and their priority is resolved. If certain conditions are met then the hardware will exe-
cute an internally generated LCALL instruction which will vector the process to the appropriate inter-
rupt 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 IE, IP, IPH, XICON 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 re-
peated 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 poll-
ing cycle is new.
The processor responds to a valid interrupt by executing an LCALL instruction to the appropriate ser-
vice 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 hardware LCALL behaves exactly like the soft-
ware 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 address of vector for the different sources are as shown on the below
table. 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 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.
Each interrupt source can be individually enabled or disabled by setting or clearing a bit in registers IE.
The IE register also contains a global disable bit, EA, which disables all interrupts at once.
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Publication Release Date: Jun 9, 2015
Revision A13