SyncMOS Technologies Inc.

SM89T16R1

8-Bits Micro-controller

With 64KB Flash ROM & IKB RAM & Two UART & RTC & ADC & PWM embedded

Specifications subject to change without notice contact your sales representatives for the most recent information.

SM89T16R1 V1.0 JANUARY 2005

30

Economy Mode

The power consumption of microcontroller relates to operating frequency. The SM89T16R1 offers an Economy mode

to reduce the internal clock rate dynamically without external components. By default, one machine cycle needs 4

clocks. In Economy mode, software can select 4, 64, or 1024 clocks per machine cycle. It keeps the CPU operating a

acceptable speed but eliminates the power consumption. In the Idle mode, the clock of the core logic is stopped, but

all clocked peripherals such as timer are still running at a rate of clock/4. In the Economy mode, all clocks peripherals

run at the same reduced clocks rate as in core logic. So the Economy mode may provide lower power consumption

than Idle mode.

Software invokes the Economy mode by setting the appropriate bits in the SFRs. Setting the bits CD0 (PMR.6), CD1

(PMR.7) decides the instruction cycle rate as below:

PMR ($D1H)

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

CD1

CD0

XTOFF

CD1

CD0

Clocks/machine cycle

00

Reserved

01

4

10

64

11

1024

Change Clock

Test Internal RC oscillator and External crystal switching

EXIF ($91H)

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

IE5

IE4

IE3

IE2

XT/~RG

IE5: When set to ‘1’, external interrupt 5 flag.

IE4: When set to ‘1’, external interrupt 4 flag.

IE3: When set to ‘1’, external interrupt 3 flag.

IE2: When set to ‘1’, external interrupt 2 flag.

XT/~RG: When set to ‘1’, the MCU used External Crystal.

When clear to ‘0’, the MCU used Internal RC Oscillator

This selection of instruction rate is going to take effect after a delay of one instruction cycle. Switching to divide by

64 or 1024 mode must first go from divide by 4 modes. This means software cannot switch directly between clock/64

and clock/1024 mode. The CPU has to return clock/4 mode first, then go to clock/64 or clock/1024 mode.

The SM89T16R1 allows the user to use internal RC oscillator instead of external crystal. Setting the XT/~RG bit

(EXIF.3) selects the crystal or RC oscillator as the clock source. When invoking RC oscillator in Economy mode,

software may set the XTOFF bit to turn off the crystal amplifier for saving power. The CPU would run at the clock

rate of approximately 2-4 MHz divided by 4, 64 or 1024. The RC oscillator is not precise so that cannot be invoked to

the operation that needs the accurate time-base such as serial communication. If crystal amplifier is disabled and RC

oscillator is present clock source, software must first clear the XTOFF bit to turn on crystal amplifier before switch to

crystal operation.

PMR ($D1H)

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

CD1

CD0

XTOFF

XTOFF: External Crystal off; if the XT/~RG bit set to 1, this bit (XTOFF) don’t care.