SH7708 datasheet(175/633 Pages) RENESAS

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Section 9 On-Chip Oscillation Circuits

9.1

Overview

The clock pulse generator (CPG) supplies all clocks to the processor and controls the power-down

modes. The watchdog timer (WDT) is a single-channel timer that counts the clock settling time

and is used when clearing standby mode and temporary standbys, such as frequency changes. It

can also be used as an ordinary watchdog timer or interval timer.

9.1.1

Features

The CPG has the following features:

• Six clock modes: Selection of six clock modes for different frequency ranges, power

consumption, direct crystal input, and external clock input.

• Three clocks generated independently: An internal clock for the CPU, cache, and TLB (Iφ); a

peripheral clock (P

φ) for the on-chip supporting modules; and a bus clock (CKI0) for the

external bus interface.

• Frequency change function: Internal and peripheral clock frequencies can be changed

independently using the PLL circuit and divider circuit within the CPG. Frequencies are

changed by software using frequency control register (FRQCR) settings.

• PLL on/off function: Power consumption can be decreased by stopping the PLL circuit when

operating at low frequencies.

• Power-down mode control: The clock can be stopped for sleep mode and standby mode and

specific modules can be stopped using the module standby function.

The WDT has the following features:

• Can be used to ensure the clock settling time: Use the WDT to cancel standby mode and the

temporary standbys which occur when the clock frequency is changed.

• Can switch between watchdog timer mode and interval timer mode.

• Generates internal resets in watchdog timer mode: Internal resets occur after counter overflow.

Selection of power-on reset or manual reset.

• Generates interrupts in interval timer mode: Internal timer interrupts occur after counter

overflow.

• Selection of eight counter input clocks. Eight clocks (×1 to ×1/4096) can be obtained by

dividing the peripheral clock.

SH7708 数据表(PDF) 175 Page - Renesas Technology Corp