SH7059 Datasheet, PDF (428/1042 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer

13. Watchdog Timer (WDT)
• Bit 7—Overflow Flag (OVF): Indicates that TCNT has overflowed from H'FF to H'00 in interval timer mode. This flag
is not set in the watchdog timer mode.
Bit 7: OVF
0
1
Description
No overflow of TCNT in interval timer mode
[Clearing condition]
When 0 is written to OVF after reading OVF
TCNT overflow in interval timer mode
(Initial value)
• Bit 6—Timer Mode Select (WT/IT): Selects whether to use the WDT as a watchdog timer or interval timer. When
TCNT overflows, the WDT either generates an interval timer interrupt (ITI) or generates a WDTOVF signal,
depending on the mode selected.
Bit 6: WT/IT
0
1
Description
Interval timer mode: interval timer interrupt (ITI) request to the CPU when TCNT overflows
(Initial value)
Watchdog timer mode: WDTOVF signal output externally when TCNT overflows. (Section
13.2.3, Reset Control/Status Register (RSTCSR), describes in detail what happens when
TCNT overflows in watchdog timer mode.)
• Bit 5—Timer Enable (TME): Enables or disables the timer.
Bit 5: TME
0
1
Description
Timer disabled: TCNT is initialized to H'00 and count-up stops
(Initial value)
Timer enabled: TCNT starts counting. A WDTOVF signal or interrupt is generated when
TCNT overflows.
• Bits 4 and 3—Reserved: These bits are always read as 1. The write value should always be 1.
• Bits 2 to 0—Clock Select 2 to 0 (CKS2 to CKS0): These bits select one of eight internal clock sources for input to
TCNT. The clock signals are obtained by dividing the frequency of the system clock (φ).
Description
Bit 2: CKS2 Bit 1: CKS1 Bit 0: CKS0 Clock Source
Overflow Interval* (φ = 80 MHz)
0
0
0
φ/2 (Initial value)
6.4 µs
0
0
1
φ/64
204.8 µs
0
1
0
φ/128
409.6 µs
0
1
1
φ/256
0.8 ms
1
0
0
φ/512
1.6 ms
1
0
1
φ/1024
3.3 ms
1
1
0
φ/4096
13.1 ms
1
1
1
φ/8192
26.2 ms
Note: * The overflow interval listed is the time from when the TCNT begins counting at H'00 until an overflow occurs.
Rev.3.00 Mar. 12, 2008 Page 338 of 948
REJ09B0177-0300