SH7713 Datasheet, PDF (368/904 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7700 Series

Section 11 On-Chip Oscillation Circuits
11.8.2 Changing Frequency
To change the frequency used by the PLL, use the WDT. When changing the frequency only by
switching the divider, do not use the WDT.
1. Before changing the frequency, always clear the TME bit in WTCSR to 0. When the TME bit
is 1, an erroneous reset or interval timer interrupt may be generated when the count overflows.
2. Set the type of count clock used in the CKS2 to CKS0 bits in WTCSR and the initial values for
the counter in WTCNT. These values should ensure that the time till count overflow is longer
than the clock oscillation settling time.
3. When the frequency control register (FRQCR) is written, the processor stop temporarily. The
WDT starts counting.
4. When the WDT count overflows, the CPG resumes supplying the clock and the processor
resumes operation. The WOVF flag in WTCSR is not set at this time.
5. The counter stops at the values H'00.
6. Before changing the WTCNT after the execution of the frequency change instruction, always
confirm that the value of the WTCNT is H'00 by reading the WTCNT.
11.8.3 Using Watchdog Timer Mode
1. Set the WT/IT bit in WTCSR to 1, set the reset type in the RSTS bit, set the type of count
clock in the CKS2 to CKS0 bits, and set the initial value of the counter in WTCNT.
2. Set the TME bit in WTCSR to 1 to start the count in watchdog timer mode.
3. While operating in watchdog timer mode, rewrite the counter periodically to H'00 to prevent
the counter from overflowing.
4. When the counter overflows, the WDT sets the WOVF flag in WTCSR to 1 and generates the
type of reset specified by the RSTS bit. The counter then resumes counting.
11.8.4 Using Interval Timer Mode
When operating in interval timer mode, interval timer interrupts are generated at every overflow of
the counter. This enables interrupts to be generated at set periods.
1. Clear the WT/IT bit in WTCSR to 0, set the type of count clock in the CKS2 to CKS0 bits, and
set the initial value of the counter in WTCNT.
2. Set the TME bit in WTCSR to 1 to start the count in interval timer mode.
3. When the counter overflows, the WDT sets the IOVF flag in WTCSR to 1 and an interval
timer interrupt request is sent to INTC. The counter then resumes counting.
Rev.1.50 Aug. 30, 2006 Page 328 of 860
REJ09B0288-0150