2 POWER SUPPLY, RESET, AND CLOCKS
2-2
Seiko Epson Corporation
S1C31D50/D51 TECHNICAL MANUAL
(Rev. 2.00)
2.1.3 V
D1
Regulator Operation Mode
The V
D1
regulator supports two operation modes, normal mode and economy mode. Setting the V
D1
regulator into
economy mode at light loads helps achieve low-power operations. Table 2.1.3.1 lists examples of light load condi-
tions in which economy mode can be set.
Table 2.1.3.1 Examples of Light Load Conditions in which Economy Mode Can be Set
Light load condition
Exceptions
SLEEP mode (when all oscillators are stopped, or OSC1 only is active) When a clock source except for
OSC1 is active
HALT mode (when OSC1 only is active)
RUN mode (when OSC1 only is active)
The V
D1
regulator also supports automatic mode in which the hardware detects a light load condition and automati-
cally switches between normal mode and economy mode. Use the V
D1
regulator in automatic mode when no special
control is required.
2.1.4 V
D1
Regulator Voltage Mode
The V
D1
regulator supports two voltage modes, mode0 and mode1.
When the IC runs with a low-speed clock, setting the V
D1
regulator into mode1 reduces power consumption.
When the voltage mode is switched, the system clock source automatically stops operating and it resumes operating
after the voltage has stabilized. Table 2.1.4.1 shows the stop period of the system clock.
Table 2.1.4.1 System Clock Stop Period After Switching Voltage Mode
System clock
Stop period
IOSC
4,096 cycles
OSC1
Number of cycles set using the CLGOSC1.OSC1WT[1:0] bits
Procedure to switch from mode0 to mode1
1. Set the MODEN bits of the peripheral circuits to 0.
(Stop using peripheral circuits)
2. Write 0x0096 to the SYSPROT.PROT[15:0] bits.
(Remove system protection)
3. Switch the system clock to a low-speed clock (OSC1, IOSC 1.8 MHz or 0.9 MHz).
4. Stop OSC3 and EXOSC.
5. Configure the following PWGACTL register bits.
- Set the PWGACTL.REGSEL bit to 0.
(Switch to mode1)
- Set the PWGACTL.REGDIS bit to 1. (Discharge)
- Set the PWGACTL.REGMODE[1:0] bits to 0x2.
(Set to normal mode)
6. Configure the following PWGACTL register bits after the system clock supply has resumed.
- Set the PWGACTL.REGDIS bit to 0.
(Stop discharging)
- Set the PWGACTL.REGMODE[1:0] bits to 0x0.
(Set to automatic mode)
7. Write a value other than 0x0096 to the SYSPROT.PROT[15:0] bits. (Set system protection)
Procedure to switch from mode1 to mode0
1. Set the MODEN bits of the peripheral circuits to 0.
(Stop using peripheral circuits)
2. Write 0x0096 to the SYSPROT.PROT[15:0] bits.
(Remove system protection)
3. Configure the following PWGACTL register bits.
- Set the PWGACTL.REGSEL bit to 1.
(Switch to mode0)
- Set the PWGACTL.REGMODE[1:0] bits to 0x2.
(Set to normal mode)
4. Set the PWGACTL.REGMODE[1:0] bits to 0x0
after the system clock supply has resumed.
(Set to automatic mode)
5. Switch the system clock to a high-speed clock.
6. Write a value other than 0x0096 to the SYSPROT.PROT[15:0] bits. (Set system protection)