Datasheet

Section 15 Watchdog Timer
(WDT1 is not available in the H8S/2695)
R01UH0166EJ0600 Rev. 6.00 Page 709 of 1434
Mar 02, 2011
H8S/2633 Group, H8S/2633 F-ZTAT
TM
,
H8S/2633R F-ZTAT
TM
, H8S/2695
Bit 7—Overflow Flag (OVF): Indicates that TCNT has overflowed from H'FF to H'00.
Bit 7
OVF Description
0 [Clearing conditions] (Initial value)
• Cleared when 0 is written to the TME bit (Only applies to WDT1)
• Cleared by reading TCSR when OVF = 1, then writing 0 to OVF
1 [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.
In interval timer mode, to clear OVF flag in WOVI handling routine, reead TCSR when OVF = 1,
then write with 0 to OVF, as stated above.
When WOVI is masked and OVF flag is poling, if contention between OVF flag set and TCSR
read is occurred, OVF = 1 is read but OVF can not be cleared by writing with 0 to OVF.
In this case, reading TCSR when OVF = 1 two times meet the requirements of OVF clear
condition. Please read TCSR when OVF = 1 two times before writing with 0 to OVF.
Bit 6—Timer Mode Select (WT/IT): Selects whether the WDT is used as a watchdog timer or
interval timer. When TCNT overflows, WDT0 generates the WDTOVF signal when in watchdog
timer mode, or a WOVI interrupt request to the CPU when in interval timer mode. WDT1
*
generates a reset or NMI interrupt request when in watchdog timer mode, or a WOVI interrupt
request to the CPU when in interval timer mode.
Note: * This function is not available in the H8S/2695.
WDT0 Mode Select
WDT0
WT/IT Description
0 Interval timer mode: WDT0 requests an interval timer interrupt (WOVI)
from the CPU when the TCNT overflows. (Initial value)
1 Watchdog timer mode: WDT0 outputs a WDTOVF signal when the TCNT overflows.
*
Note: * For details on a TCNT overflow in watchdog timer mode, see section 15.2.3, Reset
Control/Status Register (RSTCSR).