HD6417705 Datasheet, PDF (328/739 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7700 Series

9.5 Changing Frequency
The frequency of the internal clock and peripheral clock can be changed either by changing the
multiplication rate of PLL circuit 1 or by changing the division rates of divider 1. All of these are
controlled by software through the frequency control register. The methods are described below.
9.5.1 Changing Multiplication Rate
A PLL settling time is required when the multiplication rate of PLL circuit 1 is changed. The on-
chip WDT counts the settling time.
1. In the initial state, the multiplication rate of PLL circuit 1 is 1.
2. Set a value that will become the specified oscillation settling time in the WDT and stop the
WDT. The following must be set:
WTCSR.TME = 0: WDT stops
WTCSR.CKS[2:0]: Division ratio of WDT count clock
WTCNT: Initial counter value
3. Set the desired value in the STC[1:0] bits. The division ratio can also be set in the IFC[1:0] bits
and PFC[1:0] bits.
4. The processor pauses internally and the WDT starts incrementing. The internal and peripheral
clocks both stop and the WDT is supplied with the clock. The clock will continue to be output
at the CKIO pin.
5. Supply of the clock that has been set begins at WDT count overflow, and the processor begins
operating again. The WDT stops after it overflows.
9.5.2 Changing Division Ratio
The WDT will not count unless the multiplication rate is changed simultaneously.
1. In the initial state, IFC[1:0] = 00 and PFC[1:0] = 11.
2. Set the IFC[1:0], PFC[1:0] bits to the new division ratio. The values that can be set are limited
by the clock mode and the multiplication rate of PLL circuit 1. Note that if the wrong value is
set, the processor will malfunction.
3. The clock is immediately supplied at the new division ratio.
9.5.3 Modification of Clock Operating Mode
The values of the mode control pins (MD2 to MD0) that define a clock-operating mode are
reflected at power-on reset.
Rev. 2.00, 09/03, page 282 of 690