HD6417618A datasheet(235/646 Pages) RENESAS

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Section 8 Clock Pulse Generator (CPG)

Rev. 6.00 Jun. 12, 2007 Page 203 of 610

REJ09B0131-0600

8.5.2

Changing Division Ratio

The WDT will not count unless the multiplication ratio is changed simultaneously.

1. In the initial state, PFC2 to PFC0 = 011.

2. Set the desired values in bits PFC2 to PFC0 while the MDCHG bit in STBCR is 0. The values

that can be set are limited by the clock mode and the multiplication ratio of PLL circuit 1. Note

that if the wrong value is set, this LSI will malfunction.

3. The clock is immediately changed to the new division ratio.

Note:

When the MDCHG bit in STBCR is set to 1, changing the FRQCR value has no effect on

the operation immediately. For details, see section 8.5.3, Changing Clock Operating

Mode.

8.5.3

Changing Clock Operating Mode

The values of the mode control pins (MD2 to MD0) that define a clock operating mode are fetched

at a power-on reset and software standby while the MDCHG bit in STBCR is set to 1 register.

Even if changing the FRQCR with the MDCHG bit set to 1, the clock mode cannot immediately

be changed to the specified clock mode. This change can be reflected as a multiplication ratio or a

division ratio after leaving software standby mode to change operating modes. Reducing the PLL

settling time without changing again the multiplication ratio after the operating mode changing is

possible by the use of this.

The procedures for the mode change using software standby mode are described below.

1. Set bits MD2 to MD0 to the desired clock operating mode.

2. Set both the STBY and MDCHG bits in STBCR to 1.

3. Set the adequate value to the WDT so that the given oscillation settling time can be satisfied.

Then stop the WDT.

4. Set FRQCR to the desired mode. Set bits STC2 to STC0 to the desired multiplication ratio. At

this time, a division ratio can be set in bits PFC2 to PFC0. During the operation before the

mode change, the clock cannot be changed to the specified clock.

5. Enter software standby mode using the SLEEP instruction.

6. Leave software standby mode using an interrupt.

7. After leaving software standby mode, this LSI starts the operation with the value of FRQCR

that has been set before the mode change.

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