SH7018 datasheet(59/431 Pages) RENESAS

59 / 431 page

Section 4 Clock Pulse Generator (CPG)

4.1

Overview

The clock pulse generator (CPG) supplies clock pulses within the SH7018 and to external devices.

The SH7018’s CPG operates the SH7018 at a frequency equal to the oscillation frequency of the

crystal resonator. The CPG is composed of an oscillator and a duty adjustment circuit (figure 4.1).

There are two ways of generating a clock with the CPG: by connecting a crystal resonator, or by

inputting an external clock.

EXTAL

CPG

XTAL

Internal

clock (

φ)

Oscillator

Duty adjustment

circuit

CK (system

clock)

Figure 4.1 CPG Block Diagram

4.2

Clock Source

Either a crystal resonator or an external clock can be selected as the clock pulse source.

4.2.1

Crystal Resonator Connection

Circuit Configuration: Figure 4.2 shows the method of connecting a crystal resonator. Use the

damping resistance (Rd) shown in table 4.1. An AT-cut parallel-resonance type crystal resonator

with the same frequency as the system clock (CK) should be used. Load capacitors (C

L1, CL2) must

be connected as shown in the figure.

The clock pulses generated by the crystal resonator and internal oscillator are sent to the duty

adjustment circuit. After the duty has been adjusted, the pulses are supplied within the SH7018

chip and to external devices.

SH7018 Datasheet(PDF) 59 Page - Renesas Technology Corp