Rev. 1.0, 09/02, page 284 of 568
13.2 Register
Descriptions
The WDT has the following three registers. To prevent accidental overwriting, TCSR, TCNT, and
RSTCSR have to be written to by a different method to normal registers. For details, refer to
section 13.5.1, Notes on Register Access.
•
Timer control/status register (TCSR)
•
Timer counter (TCNT)
•
Reset control/status register (RSTCSR)
13.2.1
Timer Counter (TCNT)
TCNT is an 8-bit readable/writable up-counter. TCNT is initialized to H
′
00 by a reset, when the
TME bit in TCSR is cleared to 0.
13.2.2
Timer Control/Status Register (TCSR)
TCSR is an 8-bit readable/writable register. Its functions include selecting the clock source to be
input to TCNT, and selecting the timer mode.
Bit
Bit Name
Initial Value
R/W
Description
7 OVF
0
R/(W)
*
Overflow
Flag
Indicates that TCNT has overflowed. Only a write
of 0 is permitted, to clear the flag.
[Setting condition]
When TCNT overflows (changes from H
′
FF to
H
′
00)
When internal reset request generation is selected
in watchdog timer mode, OVF is cleared
automatically by the internal reset.
[Clearing conditions]
Cleared by reading TCSR when OVF = 1, then
writing 0 to OVF
6 WT/
IT
0
R/W
Timer Mode Select
Selects whether the WDT is used as a watchdog
timer or interval timer.
0: Interval timer mode
1: Watchdog timer mode
Содержание H8S/2627
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