Pll Circuit; Medium-Speed Clock Divider; Bus Master Clock Selection Circuit - Hitachi H8S/2628 Hardware Manual

20.3

PLL Circuit

The PLL circuit multiplies the frequency of the clock from the oscillator by a factor of 1, 2, or 4.
The multiplication factor is set by the STC0 bit and the STC1 bit in LPWRCR. The phase of the
rising edge of the internal clock is controlled so as to match that at the EXTAL pin.
When the multiplication factor of the PLL circuit is changed, the operation varies according to the
setting of the STCS bit in SCKCR.
When STCS = 0, the setting becomes valid after a transition to software standby mode. The
transition time count is performed in accordance with the setting of bits STS0 to STS2 in SBYCR.
For details on SBYCR, refer to section 21.1.1, Standby Control Register (SBYCR).
1. The initial PLL circuit multiplication factor is 1.
2. STS0 to STS2 are set to give the specified transition time.
3. The target value is set in STC0 and STC1, and a transition is made to software standby mode.
4. The clock pulse generator stops and the value set in STC0 and STC1 becomes valid.
5. Software standby mode is cleared, and a transition time is secured in accordance with the
setting in STS0 to STS2.
6. After the set transition time has elapsed, this LSI resumes operation using the target
multiplication factor.
If a PC break is set for the SLEEP instruction, software standby mode is entered and break
exception handling is executed after the oscillation settling time. In this case, the instruction
following the SLEEP instruction is executed after execution of the RTE instruction. When STCS =
1, this LSI operates on the changed multiplication factor immediately after bits STC0 and STC1
are rewritten.
20.4

Medium-Speed Clock Divider

The medium-speed clock divider divides the system clock to generate φ/2, φ/4, φ/8, φ/16, and
φ/32.
20.5

Bus Master Clock Selection Circuit

The bus master clock selection circuit selects the clock supplied to the bus master by setting the
bits SCK 2 to 0 in SCKCR. The bus master clock can be selected from high-speed mode, or
medium-speed clocks (φ/2, φ/4, φ/8, φ/16, φ/32).
Rev. 1.0, 09/02, page 473 of 568