SIC63616-(Rev. 1.0) NO. P39
3240-0412
4.4 Oscillation Circuit
4.4.1 Configuration of oscillation circuit
The S1C63616 is configured as a twin clock system with two internal oscillation circuits (OSC1 and OSC3).
The OSC1 oscillation circuit generates the main-clock (Typ. 32.768 kHz) for low-power operation and the
OSC3 oscillation circuit generates the sub-clock (Max. 4.2 MHz) to run the CPU and some peripheral cir-
cuits in high speed.
Figure 4.4.1.1 shows the configuration of the oscillation circuit.
To CPU
OSC1
oscillation circuit
Clock
switch
OSC3
oscillation circuit
To peripheral
circuits
OSCC
Oscillation circuit
control signal
CLKCHG
CPU clock
selection signal
To some peripheral
circuits
SLEEP
status
Prescaler
(f
OSC1
)
(f
OSC3
)
Fig. 4.4.1.1 Oscillation system block diagram
At initial reset, OSC1 oscillation circuit is selected as the CPU operating clock source. The S1C63616 allows
the software to turn the OSC3 oscillation circuit on and off, and to switch the system clock between OSC3
and OSC1. The OSC3 oscillation circuit is used when the CPU and some peripheral circuits need high speed
operation. Otherwise, use the OSC1 oscillation circuit to generate the operating clock and stop the OSC3
oscillation circuit to reduce current consumption.
Note: The S1C63616 supports the SLEEP function and both the OSC1 and OSC3 oscillation circuits
stop oscillating when the CPU enters SLEEP mode. To prevent the CPU from a malfunction when it
resumes operating from SLEEP mode, switch the CPU clock to OSC1 before placing the CPU into
SLEEP mode.
4.4.2 Mask option
The OSC1 oscillator type is fixed at crystal.
For the OSC3 oscillator type, either ceramic or CR (external R) can be selected.