
R8C/14 Group, R8C/15 Group 20. Precautions
Rev.2.10 Jan 19, 2006 Page 236 of 253
REJ09B0164-0210
20.2 Interrupts
20.2.1 Reading Address 00000h
Do not read the address 00000h by a program. When a maskable interrupt request is acknowledged,
the CPU reads interrupt information (interrupt number and interrupt request level) from 00000h in the
interrupt sequence. At this time, the acknowledged interrupt IR bit is set to “0”.
If the address 00000h is read in a program, the IR bit for the interrupt which has the highest priority
among the enabled interrupts is set to “0”. This may cause a problem that the interrupt is canceled, or
an unexpected interrupt is generated.
20.2.2 SP Setting
Set any value in the SP before an interrupt is acknowledged. The SP is set to “0000h” after reset.
Therefore, if an interrupt is acknowledged before setting any value in the SP, the program may run
out of control.
20.2.3 External Interrupt and Key Input Interrupt
Either an “L” level or an “H” level of at least 250ns width is necessary for the signal input to the INT0
to INT3 pins and KI0 to KI3 pins regardless of the CPU clock.s
20.2.4 Watchdog Timer Interrupt
Reset the watchdog timer after a watchdog timer interrupt is generated.
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