5 POWER-DOWN CONTROL

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)/

OSC3

OSC1

OSC3

 

Power control register(0x40180)

 

 

 

High-speed (OSC3) oscillation ON/OFF control

SOSC3(D1)/

ON

OFF

ON

 

Power control register(0x40180)

 

 

 

System clock division ratio selection

CLKDT(D[7:6])/

"11" = 1/8

1/1

 

Power control register(0x40180)

"10" = 1/4

 

 

 

"01" = 1/2

 

 

 

"00" = 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.

S1C33210 PRODUCT PART

EPSON

A-63