Epson S1C17M20 Technical Manual page 29

2 POWER SUPPLY, RESET, AND CLOCKS
The IOSC oscillator circuit output clock IOSCCLK is used as SYSCLK at booting. For the oscillation charac-
teristics, refer to "IOSC oscillator circuit characteristics" in the "Electrical Characteristics" chapter.
OSC1 oscillator circuit
The OSC1 oscillator circuit is a low-power oscillator circuit that allows software to select the oscillator type
from two different types shown below. Figure 2.3.3.2 shows the configuration of the OSC1 oscillator circuit.
Crystal oscillator
This oscillator circuit includes a gain-controlled oscillation inverter and a variable gate capacitor allowing use
of various crystal resonators (32.768 kHz typ.) with ranges from cylinder type through surface-mount type.
The oscillator circuit also includes a feedback resistor and a drain resistor, so no external parts are required
except for a crystal resonator. The embedded oscillation stop detector, which detects oscillation stop and re-
starts the oscillator, allows the system to operate in safety under adverse environments that may stop the oscil-
lation. The oscillation startup control circuit operates for a set period of time after the oscillation is enabled to
assist the oscillator in initiating, this makes it possible to use a low-power resonator that is difficult to start up.
Note: Depending on the circuit board or the crystal resonator type used, an external gate capacitor C
and a drain capacitor C
Internal oscillator
This 32 kHz oscillator circuit operates without any external parts.
When the internal oscillator circuit is used, the OSC1 and OSC3 pins must be left open.
OSC1 oscillator circuit
Selector
Crystal oscillator
External gate
Internal variable
capacitor C
G1
OSC1
gate capacitor C
X'tal1
OSC2
External drain
capacitor C
D1
Internal drain capacitor C
Internal oscillator
For the recommended parts and the oscillation characteristics, refer to the "Basic External Connection Dia-
gram" chapter and "OSC1 oscillator circuit characteristics" in the "Electrical Characteristics" chapter, respec-
tively.
2-6
IOSC oscillator circuit
IOSCEN
Oscillation
Clock
stabilization
oscillator
waiting circuit
IOSCSTAIE
Interrupt
control circuit
Figure 2.3.3.1 IOSC Oscillator Circuit Configuration
may be required.
D1
OSC1SELCR
OSC1EN
OSC1BUP INV1N[1:0] INV1B[1:0]
Oscillation startup
control circuit
Gain-controlled
oscillation
inverter
GI1
CGI1[2:0]
Feedback Drain
resistor R resistor R
F1
DI1
Clock
oscillator
Figure 2.3.3.2 OSC1 Oscillator Circuit Configuration
Seiko Epson Corporation
IOSCCLK
IOSCSTAIF
OSC1 oscillator circuit
voltage regulator
OSDRB OSDEN
Restart
signal Oscillation
stop detector
OSC1WT[1:0]
Noise filter Oscillation
stabilization
waiting circuit
OSC1STPIE
control circuit
OSC1STAIE
D1
Interrupt
controller
OSC1CLK
Interrupt
OSC1STPIF
OSC1STAIF
S1C17M20/M21/M22/M23/M24/M25
TECHNICAL MANUAL (Rev. 1.0)
G1
Interrupt
controller