SH7021 datasheet(107/509 Pages) RENESAS

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RENESAS 89

Section 7 Clock Pulse Generator (CPG)

7.1

Overview

The SuperH microcomputer has a built-in clock pulse generator (CPG) that supplies the LSI and

external devices with a clock pulse. The CPG makes the LSI run at the oscillation frequency of the

crystal resonator. The CPG consists of an oscillator and a duty cycle correcting circuit (figure 7.1).

The CPG can be made to generate a clock signal by connecting it to a crystal resonator or by

inputting an external clock. (The CPG is halted in standby mode.)

XTAL

EXTAL

System clock

Oscillator

Duty correcting

circuit

Internal

clock (

φ)

CPG

Figure 7.1 Block Diagram of the Clock Pulse Generator

7.2

Clock Source

Clock pulses can be supplied from a connected crystal resonator or an external clock.

7.2.1

Connecting a Crystal Resonator

Circuit Configuration: A crystal resonator can be connected as shown in figure 7.2. Use the

damping resistance Rd shown in table 7.1. Use an AT-cut parallel resonating crystal with a

frequency equal to the system clock (CK) frequency. Connect load capacitors (CL1 and CL2) as

shown in the figure. The clock pulse produced by the crystal resonator and internal pulse generator

is sent to the duty cycle correction circuit where its duty cycle is corrected. It is then supplied to

the LSI and to external devices.

SH7021 Datasheet(PDF) 107 Page - Renesas Technology Corp