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Section 14 Watchdog Timer (WDT)
14.5
Interrupt Sources
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.
When the NMI interrupt request is selected in watchdog timer mode, an NMI interrupt request is
generated by an overflow
Table 14.3 WDT Interrupt Source
Name
Interrupt Source
WOVI
TCNT overflow
14.6
Usage Notes
14.6.1
Notes on Register Access
The watchdog timer's registers, TCNT and TCSR differ from other registers in being more
difficult to write to. The procedures for writing to and reading from these registers are given
below.
(1)
Writing to TCNT and TCSR (Example of WDT_0)
These registers must be written to by a word transfer instruction. They cannot be written to by a
byte transfer instruction.
TCNT and TCSR both have the same write address. Therefore, satisfy the relative condition
shown in figure 14.5 to write to TCNT or TCSR. To write to TCNT, the higher bytes must contain
the value H'5A and the lower bytes must contain the write data before the transfer instruction
execution. To write to TCSR, the higher bytes must contain the value H'A5 and the lower bytes
must contain the write data.
Rev. 1.00 Apr. 28, 2008 Page 400 of 994
REJ09B0452-0100
Interrupt Flag
OVF
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