Epson S1C33210 Technical Manual page 77

Switching over the system clocks
Normally, the system is clocked by the high-speed (OSC3) oscillation clock. If high-speed operation is
unnecessary, switch the system clock to the low-speed (OSC1) oscillation clock and turn off the high-speed
(OSC3) oscillation circuit. This helps to reduce current consumption. However, if DRAM is connected directly
to the device, note that the refresh function is also turned off.
Even during operation using the high-speed (OSC3) oscillation clock, power reduction can also be achieved
through the use of a system clock derived from the OSC3 clock by dividing it (1/1, 1/2, 1/4, or 1/8).
System clock switch over
High-speed (OSC3) oscillation ON/OFF control
System clock division ratio selection
Turning off the prescaler and peripheral circuits
Current consumption can be reduced by turning off the peripheral circuits operating at high speed as much as
possible. This applies to the following peripheral circuits.
1) Blocks that use an operating clock generated by the prescaler
• 16-bit programmable timers 0 to 5 (watchdog timer)
• 8-bit programmable timers 0 to 5 (DRAM refresh, serial interface)
• A/D converter
2) Blocks that use the clock supplied to the prescaler (the prescaler source clock)
• 16-bit programmable timers 0 to 5 (watchdog timer)
• 8-bit programmable timers 0 to 5 (DRAM refresh)
• A/D converter
• Serial interface
• Ports
If none of the blocks in groups 1 and 2 above are used, turn off the prescaler. If any of the blocks in groups 1 and
2 above are used, do not turn off the prescaler. Turning off the prescaler turns off the clock signal supplied to the
blocks in group 2 above. Also, if only some of the circuits in group 1 above are used, turn off all the other
circuits and stop clock supply from the prescaler to those circuits.
The table below shows prescaler operation control and control of clock supply to these blocks from the
prescaler.
S1C33210 PRODUCT PART
Function Control bit
CLKCHG(D2)/
Power control register(0x40180)
SOSC3(D1)/
Power control register(0x40180)
CLKDT(D[7:6])/
Power control register(0x40180)
EPSON
5 POWER-DOWN CONTROL
"1" "0" Default
OSC3 OSC1 OSC3
ON OFF ON
"11" = 1/8 1/1
"10" = 1/4
"01" = 1/2
"00" = 1/1
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