Hyundai Micro Electronics
GMS81C2020/GMS81C2120
The following method is used to save/restore the general-
purpose registers.
General-purpose register save/restore using push and pop
instructions;
Example: Register save using push and pop instructions
main task
INTxx: PUSH
PUSH
A
X
Y
;SAVE ACC.
;SAVE X REG.
;SAVE Y REG.
acceptance of
interrupt
interrupt
service task
PUSH
saving
registers
interrupt processing
POP
POP
POP
RETI
Y
X
A
;RESTORE Y REG.
;RESTORE X REG.
;RESTORE ACC.
;RETURN
restoring
registers
interrupt return
19.2 BRK Interrupt
Software interrupt can be invoked by BRK instruction,
which has the lowest priority order.
Interrupt vector address of BRK is shared with the vector
of TCALL 0 (Refer to Program Memory Section). When
BRK interrupt is generated, B-flag of PSW is set to distin-
guish BRK from TCALL 0.
=0
B-FLAG
=1
BRK
INTERRUPT
ROUTINE
BRK or
TCALL0
Each processing step is determined by B-flag as shown in
Figure 19-4 .
TCALL0
ROUTINE
RETI
RET
Figure 19-4 Execution of BRK/TCALL0
19.3 Multi Interrupt
If two requests of different priority levels are received si-
multaneously, the request of higher priority level is ser-
viced. If requests of the interrupt are received at the same
time simultaneously, an internal polling sequence deter-
mines by hardware which request is serviced.
However, multiple processing through software for special
features is possible. Generally when an interrupt is accept-
ed, the I-flag is cleared to disable any further interrupt. But
as user sets I-flag in interrupt routine, some further inter-
rupt can be serviced even if certain interrupt is in progress.
Nov. 1999 Ver 0.0
preliminary
69
HYNIX [ HYNIX SEMICONDUCTOR ]
