Clock Pulse Generator (Cpg); Overview; Clock Source; Connecting A Crystal Resonator - Hitachi SH7032 Hardware Manual

Section 7 Clock Pulse Generator (CPG)
7.1

Overview

The SuperH microcomputer has a built-in clock pulse generator (CPG) that supplies the chip and
external devices with a clock pulse. The CPG makes the chip run at the oscillation frequency of
the crystal resonator. The CPG consists of an oscillator and a duty cycle correction 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
CK
System clock
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 (C
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 chip and to external devices.
Oscillator
Figure 7.1 Block Diagram of Clock Pulse Generator
CPG
Duty cycle
correction circuit
Internal
clock (φ)
and C ) as
L1 L2
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