6 CLOCK MANAGEMENT UNIT (CMU)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
6-3
OSC3 oscillation on/off
The OSC3 oscillator circuit stops oscillating when OSC3EN/CMU_OSCCTL register is set to 0 and starts os-
cillating when set to 1. The OSC3 oscillator circuit stops oscillating even in SLEEP mode. After an initial reset,
OSC3EN is set to 1 and the OSC3 oscillator circuit is activated.
Stabilization wait time at start of OSC3 oscillation
The OSC3 oscillator circuit incorporates an oscillation stabilization wait timer to prevent malfunctions due to
unstable clock operations at the start of OSC3 oscillation—e.g., after an initial reset or waking from SLEEP
mode when OSC3 or PLL is used as the system clock source. The OSC3 or PLL clock is not supplied to the
system until the time set for this timer has elapsed. Use OSC3WT[3:0]/CMU_OSCCTL register to select one of
16 oscillation stabilization wait times.
3.1.1 OSC3 Oscillation Stabilization Wait Time Settings
Table 6.
OSC3WT[3:0]
Oscillation stabilization wait time
0xf
128 cycles
0xe
256 cycles
0xd
512 cycles
0xc
1,024 cycles
0xb
2,048 cycles
0xa
4,096 cycles
0x9
8,192 cycles
0x8
16,384 cycles
0x7
32,768 cycles
0x6
65,536 cycles
0x5
131,072 cycles
0x4
262,144 cycles
0x3
524,288 cycles
0x2
1,048,576 cycles
0x1
2,097,152 cycles
0x0
4,194,304 cycles
(Default: 0xf)
This is set to 128 cycles (OSC3 clock) after an initial reset.
Notes: • The OSC3 oscillation stabilization wait timer cannot be used when the OSC3 oscillator is
turned on with software. Therefore, a software wait routine must be implemented.
• Oscillation stability will vary, depending on the resonator and other external components.
Carefully consider the OSC3 oscillation stabilization wait time before reducing the time. When
waking from SLEEP mode if OSC3 or PLL is used as the system clock source, set the OSC3
oscillation stabilization wait time as follows:
OSC3 oscillation stabilization wait time [cycle]
≥
OSC3 oscillation start time [s] (max.)
×
f
SYSCLK
[Hz]
f
SYSCLK
: SYSCLK frequency when the clock source is OSC3 or PLL.
Example: When OSC3 oscillation start time (max.) = 10 ms and f
SYSCLK
= 48 MHz
OSC3 oscillation stabilization wait time
≥
480,000 [cycles]
OSC3WT[3:0] should be set to 0x3 (OSC3 oscillation stabilization wait time = 524,288
cycles).
OSC1 Oscillator Circuit
6.3.2
The S1C33L26 contains an oscillator circuit (OSC1) used to generate a 32.768 kHz (typ.) clock as the clock source
for timekeeping operation of the RTC. The OSC1 clock can also be used as a power-saving operating clock for the
core system or peripheral circuits.
Structure of the OSC1 oscillator circuit
The OSC1 oscillator circuit accommodates a crystal oscillator and external clock input. As for the RTC,
RTCV
DD
is used to supply power to this circuit.