4554 Datasheet, PDF (29/138 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4554 Group
(4) Notes on External 0 interrupts
➀ Note [1] on bit 3 of register I1
When the input of the INT0 pin is controlled with the bit 3 of reg-
ister I1 in software, be careful about the following notes.
➂ Note on bit 2 of register I1
When the interrupt valid waveform of the D8/INT0 pin is changed
with the bit 2 of register I1 in software, be careful about the fol-
lowing notes.
• Depending on the input state of the D8/INT0 pin, the external 0 in-
terrupt request flag (EXF0) may be set when the bit 3 of register
I1 is changed. In order to avoid the occurrence of an unexpected
interrupt, clear the bit 0 of register V1 to “0” (refer to Figure 18➀)
and then, change the bit 3 of register I1.
In addition, execute the SNZ0 instruction to clear the EXF0 flag
to “0” after executing at least one instruction (refer to Figure
18➁).
Also, set the NOP instruction for the case when a skip is per-
formed with the SNZ0 instruction (refer to Figure 18➂).
• Depending on the input state of the D8/INT0 pin, the external 0 in-
terrupt request flag (EXF0) may be set when the bit 2 of register
I1 is changed. In order to avoid the occurrence of an unexpected
interrupt, clear the bit 0 of register V1 to “0” (refer to Figure 20➀)
and then, change the bit 2 of register I1.
In addition, execute the SNZ0 instruction to clear the EXF0 flag
to “0” after executing at least one instruction (refer to Figure
20➁).
Also, set the NOP instruction for the case when a skip is per-
formed with the SNZ0 instruction (refer to Figure 20➂).
LA 4
TV1A
LA 8
TI1A
NOP
SNZ0
NOP
; (✕✕✕02)
; The SNZ0 instruction is valid ........... ➀
; (1✕✕✕2)
; Control of INT0 pin input is changed
........................................................... ➁
; The SNZ0 instruction is executed
(EXF0 flag cleared)
........................................................... ➂
LA 4
TV1A
LA 12
TI1A
NOP
SNZ0
NOP
; (✕✕✕02)
; The SNZ0 instruction is valid ........... ➀
; (✕1✕✕2)
; Interrupt valid waveform is changed
........................................................... ➁
; The SNZ0 instruction is executed
(EXF0 flag cleared)
........................................................... ➂
✕ : these bits are not used here.
Fig. 18 External 0 interrupt program example-1
✕ : these bits are not used here.
Fig. 20 External 0 interrupt program example-3
➁ Note [2] on bit 3 of register I1
When the bit 3 of register I1 is cleared to “0”, the RAM back-up
mode is selected and the input of INT0 pin is disabled, be careful
about the following notes.
• When the key-on wakeup function of INT0 pin is not used (regis-
ter K20 = “0”), clear bits 2 and 3 of register I1 before system
enters to the RAM back-up mode. (refer to Figure 19➀).
LA 0
TI1A
DI
EPOF
POF2
; (00✕✕2)
; Input of INT0 disabled ..................... ➀
; RAM back-up
✕ : these bits are not used here.
Fig. 19 External 0 interrupt program example-2
Rev.3.00 Aug 06, 2004 page 29 of 136
REJ03B0043-0300Z