6 CLOCK MANAGEMENT UNIT (CMU)
6-4
Seiko Epson Corporation
S1C33L26 TECHNICAL MANUAL
Figure 6.3.2.1 shows the structure of the OSC1 oscillator circuit.
Low level
OSC1
RTCCLKO
RTCCLKI
External
clock
N.C.
V
SS
RTCV
DD
OSC1
(1) Crystal oscillation circuit
V
SS
RTCCLKO
RTCCLKI
(3) When not used
(2) External clock input
V
SS
RTCCLKO
RTCCLKI
C
D1
C
G1
X'tal1
R
f
R
d
3.2.1 OSC1 Oscillator Circuit
Figure 6.
For use as a crystal oscillator circuit, connect a crystal resonator X’tal1 (32.768 kHz, typ.), feedback resistor (R
f
),
two capacitors (C
G1
, C
D1
), and, if necessary, a drain resistor (R
d
) to the RTCCLKI and RTCCLKO pins and V
SS
,
as shown in the figure above.
To use an external clock, leave the RTCCLKO pin open and input an RTCV
DD
-level clock (whose duty cycle is
50%) to the RTCCLKI pin.
The oscillator frequency/input clock frequency is 32.768 kHz (typ.). Make sure the crystal resonator or external
clock used in the RTC has this clock frequency. With any other clock frequencies, the RTC cannot be used for
timekeeping purposes.
For details of oscillation characteristics and the input characteristics of external clock, see “Electrical Charac-
teristics.”
When not using the OSC1 oscillator circuit, connect the RTCCLKI pin to V
SS
and leave the RTCCLKO pin
open.
OSC1 oscillation on/off
The OSC1 oscillator circuit stops oscillating when OSC1EN/CMU_OSCCTL register is set to 0 and starts os-
cillating when set to 1. After an initial reset, OSC1EN is set to 1 and the OSC1 oscillator circuit is activated.
The OSC1 oscillator circuit does not stop oscillating in SLEEP mode.
Note: A finite time (see “Electrical Characteristics”) is required until oscillation stabilizes after the OSC1
oscillator starts oscillating. To prevent system malfunction, do not use the oscillator-derived clock
until this oscillation stabilization time elapses.
PLL
6.4
The PLL multiplies the OSC3 clock frequency by a given value to generate a source clock for high-speed operation.
PLL On/Off Control
6.4.1
PLLPOWR/CMU_PLLCTL0 register can be used to turn the PLL on or off. Setting PLLPOWR to 1 initiates PLL
operation. When initially reset, PLLPOWR is set to 0 (power-down mode), with the PLL turned off.
Notes: • Immediately after the PLL is started by setting PLLPOWR to 1, an output clock stabilization
wait time is required (see “Electric Characteristics”). After the PLL clock is stabilized, the clock
source for the system can be switched over to the PLL.
• Be sure to turn the PLL off before setting the CPU into SLEEP mode (before executing the slp
instruction).