Epson S1C33L03 User Manual

This section describes the method for controlling the system clock.

The C33 Core Block has a built-in clock generator that consists of a high-speed oscillation circuit (OSC3) and a

PLL.

The high-speed (OSC3) oscillation circuit generates the main clock for the CPU and internal peripheral circuits

(e.g., DMA, serial interface, programmable timer, and A/D converter).

Furthermore, the clock generator can input a sub clock, such as low-speed (OSC1, 32.768 kHz, Typ.) clock

generated by the Peripheral Block, for the clock timer and for operating the CPU at a low clock speed in order to

reduce current consumption.

Note: When the Peripheral Block including the low-speed (OSC1) oscillation circuit is used, the source

clocks for the CPU and the peripheral circuits (e.g., serial interface, programmable timer, and A/D
converter) can be selected between the OSC3 clock and the OSC1 clock. For details, refer to
"Setting and Switching Over the CPU Operating Clock" in this section and "Prescaler" and "Low-
Speed (OSC1) Oscillation Circuit" of the Peripheral Block.

Figure 6.1 shows the configuration of the clock generator.

High-speed (OSC3)

oscillation circuit

Clock

switch

CLKCHG

To CPU

SLEEP

OSC3
OSC4

HALT, HALT2, 

SLEEP 

SOSC3

Oscillation ON/OFF

CLKDT[1:0]

Divider

1/1 to 1/8

To BCU and DMA

HALT2, SLEEP

To peripheral circuits

To peripheral circuits

and clock timer

SLEEP

PLL

PLLC

PLLS0
PLLS1

Low-speed (OSC1)

oscillation circuit

SOSC1

Oscillation ON/OFF

OSC1
OSC2

CLG

Peripheral Block

Figure 6.1  Configuration of Clock Generator

After an initial reset, the output (OSC3 clock) of the high-speed (OSC3) oscillation circuit is set for the CPU

operating clock.

When the low-speed (OSC1) oscillation circuit is used, the CPU operating clock can be switched to the output

(OSC1 clock) of the low-speed (OSC1) oscillation circuit in a program. Furthermore, each oscillation circuit can be

stopped in a program.

If the OSC3 clock is unnecessary such as when performing clock processing only, set the OSC1 clock for operation

of the CPU and turn off the high-speed (OSC3) oscillation circuit in order to reduce current consumption. In

addition, when SLEEP mode is set, the high-speed (OSC3) oscillation circuit is turned off, greatly reducing current

consumption (no internal units except for the clock timer need to be operated).