HD64F3028F25 Datasheet, PDF (657/925 Pages) Renesas Technology Corp – Hardware Manual Renesas 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Series

Section 19 Clock Pulse Generator
19.1 Overview
The H8/3028 Group has a built-in clock pulse generator (CPG) that generates the system clock (φ)
and other internal clock signals (φ/2 to φ/4096). After duty adjustment, a frequency divider divides
the clock frequency to generate the system clock (φ). The system clock is output at the φ pin*¹ and
furnished as a master clock to prescalers that supply clock signals to the on-chip supporting
modules. Frequency division ratios of 1/1, 1/2, 1/4, and 1/8 can be selected for the frequency
divider by settings in a division control register (DIVCR)*². Power consumption in the chip is
reduced in almost direct proportion to the frequency division ratio.
Notes: 1. Usage of the φ pin differs depending on the chip operating mode and the PSTOP bit
setting in the module standby control register (MSTCR). For details, see section 20.7,
System Clock Output Disabling Function.
2. The division ratio of the frequency divider can be changed dynamically during
operation. The clock output at the φ pin also changes when the division ratio is
changed. The frequency output at the φ pin is shown below.
φ = EXTAL × n
where, EXTAL: Frequency of crystal resonator or external clock signal
n:
Frequency division ratio (n = 1/1, 1/2, 1/4, or 1/8)
19.1.1 Block Diagram
Figure 19.1 shows a block diagram of the clock pulse generator.
XTAL
EXTAL
Oscillator
Duty
adjustment
circuit
CPG
Frequency ^φ
divider
Prescalers
Division
control
register
Data bus
φ pin φ/2 to φ/4096
Figure 19.1 Block Diagram of Clock Pulse Generator
Rev. 2.00, 09/03, page 625 of 890