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12.4
Interrupts
During interval timer mode operation, an overflow generates an interval timer interrupt (WOVI).
The interval timer interrupt is requested whenever the OVF flag is set to 1 in TCSR. OVF must be
cleared to 0 in the interrupt handling routine.
Table 12.1
WDT Interrupt Source
Name
Interrupt Source
Interrupt Flag
DTC Activation
WOVI
TCNT overflow
WOVF
Impossible
12.5
Usage Notes
12.5.1
Notes on Register Access
The watchdog timer’s TCNT, TCSR, and RSTCSR registers differ from other registers in being
more difficult to write to. The procedures for writing to and reading these registers are given
below.
Writing to TCNT and TCSR
These registers must be written to by a word transfer instruction.
They cannot be written to with byte transfer instructions. Figure 12.6 shows the format of data
written to TCNT and TCSR. TCNT and TCSR both have the same write address. For a write to
TCNT, the upper byte of the written word must contain H'5A and the lower byte must contain the
write data. For a write to TCSR, the upper byte of the written word must contain H'A5 and the
lower byte must contain the write data. This transfers the write data from the lower byte to TCNT
or TCSR.
TCNT write
TCSR write
Address: H'FF74
Address: H'FF74
H'5A
Write data
15
8 7
0
H'A5
Write data
15
8 7
0
Figure 12.6 Format of Data Written to TCNT and TCSR
Writing to RSTCSR
Summary of Contents for H8S/2215 Series
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