Specifications

I-22 EPSON S1C62740 TECHNICAL HARDWARE
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Oscillation Circuit)
Oscillation Circuit4.3
Configuration of
oscillation circuit
The S1C62740 has two oscillation circuits (OSC1 and OSC3).
OSC1 is a crystal oscillation circuit that supplies the operating
clock the CPU and peripheral circuits. OSC3 is either a CR or
ceramic oscillation circuit. When processing with the S1C62740
requires high-speed operation, the CPU operating clock can be
switched from OSC1 to OSC3.
Figure 4.3.1 is the block diagram of this oscillation system.
Fig. 4.3.1
Oscillation system
Selection of either OSC1 or OSC3 for the CPU's operating clock can
be made through the software.
OSC1 oscillation
circuit
The S1C62740 has a built-in crystal oscillation circuit (OSC1
oscillation circuit). As an external element, the OSC1 oscillation
circuit generates the operating clock for the CPU and peripheral
circuitry by connecting the crystal oscillator (Typ. 32.768 kHz) and
trimmer capacitor (5–25 pF).
Figure 4.3.2 is the block diagram of the OSC1 oscillation circuit.
Fig. 4.3.2
OSC1 oscillation circuit
Oscillation circuit control signal
CPU clock selection signal
To CPU
(and serial interface)
To peripheral circuit
Clock
switch
OSC1
oscillation
circuit
OSC3
oscillation
circuit
SLEEP (during SLEEP: HIGH)
VSS
CGX
X'tal
OSC2
OSC1
R
R
DX
CDX
To CPU and
peripheral circuit
FX
VSS
SLEEP
As Figure 4.3.2 indicates, the crystal oscillation circuit can be
configured simply by connecting the crystal oscillator (X'tal) be-
tween terminals OSC1 and OSC2 to the trimmer capacitor (C
GX)
between terminals OSC1 and V
SS.
The OSC1 oscillation circuit is off in the SLEEP status.