SH7020 Datasheet, PDF (107/509 Pages) Renesas Technology Corp – SuperH™ RISC engine

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.)
CPG
XTAL
EXTAL
Oscillator
Duty correcting
circuit
Internal
clock (φ)
CK
System clock
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 (C_L1 and C_L2) 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.
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