beautypg.com

Switching over the system clocks, Turning off the prescaler and peripheral circuits – Epson S1C33210 User Manual

Page 77

background image

5 POWER-DOWN CONTROL

S1C33210 PRODUCT PART

EPSON

A-63

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).

Function

Control bit

"1"

"0"

Default

System clock switch over

CLKCHG(D2)/

Power control register(0x40180)

OSC3 OSC1 OSC3

High-speed (OSC3) oscillation ON/OFF control

SOSC3(D1)/

Power control register(0x40180)

ON

OFF

ON

System clock division ratio selection

CLKDT(D[7:6])/

Power control register(0x40180)

"11" = 1/8
"10" = 1/4
"01" = 1/2
"00" = 1/1

1/1

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.