
7 Oscillator Circuit (OSC)
S1C17003 TECHNICAL MANUAL
EPSON
7-3
OSC
7.3 OSC1 Oscillator Circuit
OSC1 is a high-precision, low-speed oscillator circuit using a 32.768 kHz crystal oscillator.
The OSC1 clock is generally used as the timer operation clock (for the clock timer, stopwatch timer, watchdog
timer, and 8-bit OSC1 timer). It reduces power consumption and can be used as the system clock instead of the
OSC3 clock when no high-speed processing is required.
Figure 7.3.1 illustrates the OSC1 oscillator circuit configuration.
VSS
OSC2
OSC1
X'tal1
CG1
SLEEP status
fOSC1
Figure 7.3.1: OSC1 oscillator circuit
A crystal oscillator (X’tal1) (typ. 32.768 kHz) should be connected between the OSC1 and OSC2 pins.
Additionally, trimmer capacitor CG1 (0 to 25 pF) should be connected between the OSC1 pin and VSS.
OSC1 oscillation on/off
The OSC1 oscillator circuit stops oscillating if OSC1EN (D1/OSC_CTL register) is set to 0 and starts
oscillating if set to 1. The OSC1 oscillator circuit stops oscillating even in SLEEP mode.
OSC1EN: OSC1 Enable Bit in the Oscillation Control (OSC_CTL) Register (D1/0x5061)
Following initial resetting, OSC1EN is set to 0, and the OSC1 oscillator circuit is halted.
Stabilization wait time at start of OSC1 oscillation
The OSC1 oscillator circuit incorporates an oscillation stabilization wait timer to prevent malfunctions due
to unstable clock operations at the start of OSC1 oscillation—for example, when power is first turned on, on
awaking from SLEEP, or when the OSC1 oscillation circuit is turned on via software. The OSC1 clock does not
feed the system for a period of 256 cycles after the start of oscillation.
OSC clock system supply wait time =< IOSC oscillation start time (max.) + OSC1 oscillation
stabilization wait time.
Pin settings when OSC1 is not used
Keep the OSC1 and OSC2 pins open.
Note: Set OSC1EN (the D1/OSC_CTL register) to 0 while the OSC1 and OSC2 pins are kept open.