SH7760 Datasheet, PDF (526/1345 Pages) Renesas Technology Corp – SuperHTM RISC engine

12.5 Frequency Changing Method
There are two methods of changing the clock frequency: by switching off and on PLL circuit 1,
and by changing the frequency division ratio of each clock. In both cases, control is performed by
software by means of FRQCR, MCKCR, and DCKDR. These methods are described below.
12.5.1 Switching between PLL Circuit 1 On/Off (When PLL Circuit 2 is Off)
When PLL circuit 1 is turned on, the oscillation stabilization time for PLL circuit 1 is required.
The oscillation stabilization time is counted by the on-chip WDT.
1. Set a value in WDT to provide the specified oscillation stabilization time, and stop the WDT.
The following settings are necessary:
TME bit in WTCSR = 0: WDT stopped
CKS2 to CKS0 bits in WTCSR: WDT count clock frequency division ratio
WTCNT: Initial counter value
2. Set the PLL1EN bit to 1.
3. This LSI operation stops temporarily, and the WDT starts counting up. The internal clock stops
and an unstable clock is output to the CKIO pin.
4. After the WDT count overflows, a clock begins to be supplied within the chip, and this LSI
resumes operation. The WDT stops after overflowing.
12.5.2 Switching between PLL Circuit 1 On/Off (When PLL Circuit 2 is On)
When PLL circuit 2 is on, the oscillation stabilization time for PLL circuit 1 and PLL circuit 2 is
required.
1. Make WDT settings as in step 1 in section 12.5.1.
2. Set the PLL1EN bit to 1.
3. This LSI operation stops temporarily, PLL circuit 1 starts oscillation, and the WDT starts
counting up. The internal clock stops and an unstable clock is output to the CKIO pin.
4. After the WDT count overflows, PLL circuit 2 starts oscillation. The WDT resumes its up-
count from the value set in step 1 above. Even during this time, the internal clock is stopped
and an unstable clock is output to the CKIO pin.
5. After the WDT count overflows, a clock begins to be supplied within the chip, and this LSI
resumes operation. The WDT stops after overflowing.
Rev. 1.0, 02/03, page 476 of 1294