HMS81008E Hynix Semiconductor, HMS81008E Datasheet - Page 54

• Manufacturer Part Number: HMS81008E
• Description: HYNIX SEMICONDUCTOR 8-BIT SINGLE-CHIP MICROCONTROLLERS
• Manufacturer: Hynix Semiconductor

A interrupt request is not accepted until the I-flag is set to “1”
even if a requested interrupt has higher priority than that of the
current interrupt being serviced.
When nested interrupt service is required, the I-flag should be set
to “1” by “EI” instruction in the interrupt service program. In this
case, acceptable interrupt sources are selectively enabled by the
individual interrupt enable flags.
Saving/Restoring General-purpose Register
During interrupt acceptance processing, the program counter and
the program status word are automatically saved on the stack, but
accumulator and other registers are not saved itself. These regis-
ters are saved by the software if necessary. Also, when multiple
interrupt services are nested, it is necessary to avoid using the
same data memory area for saving registers.
The following method is used to save/restore the general-purpose
JUNE 2001 Ver 1.00
Correspondence between vector table address for Exteranl Interrupt1
and the entry address of the interrupt service program.
0FFF8
0FFF9
External Interrupt1
Vector Table Address
H
H
System clock
Instruction Fetch
Address Bus
Data Bus
Internal Read
Internal Write
V.L. and V.H. are vector addresses.
ADL and ADH are start addresses of interrupt service routine as vector contents.
012
0E3
H
H
Figure 14-4 Timing chart of Interrupt Acceptance and Interrupt Return Instruction
0E312
0E313
Not used
PC
H
H
Entry Address
0E
2E
SP
Interrupt Processing Step
H
H
PCH
SP-1
PCL
PSW
SP-2
registers.
Example: Register save using push and pop instructions
General-purpose register save/restore using push and pop instruc-
tions;
INTxx:
V.L.
main task
V.L.
PUSH
PUSH
PUSH
interrupt processing
POP
POP
POP
RETI
ADL
V.H.
interrupt return
interrupt
acceptance of
ADH
HMS81004E/08E/16E/24E/32E
A
X
Y
Y
X
A
Interrupt Service Task
interrupt
service task
;SAVE ACC.
;SAVE X REG.
;SAVE Y REG.
;RESTORE Y REG.
;RESTORE X REG.
;RESTORE ACC.
;RETURN
New PC
OP code
saving
registers
restoring
registers
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