Aug.2007

www.eorex.com

Base Timer

Base timer is optioned from [BASE1, BASE0] and it will cause a period timer base interrupt enabled

(TBINT=1) & (TBEN=1). But the real time counter have the same clock source and it is optioned by

UCCLK.7($03H.7=CKSEL).

BASE1

BASE0

0

0

0

1

1

0

1

1

MCU clock selection

With a built-in internal RC oscillator, the MCU frequency is 4MHz ±3% @4.5V. MCU system clock

offers 4MHz, 2MHz, 1MHz, 512KHz or 256KHz by MCU clock options bit; RCSEL2~0. Please refer to

the following table.

Address

03H

bit7

bit6

bit5

bit4

bit3

bit2

bit1

bit0

Name

UCCLK

#

BASE1 BASE0

RTC1

RTC0 RCSEL2 RCSEL1 RCSEL0

Read or Write

#

W

W

W

W

W

W

W

Default Value

0

0

0

0

0

0

0

0

The MCU system clock could be switched by setting RCSEL2~0. First, pre-set RCSEL2~0 register and

then execute “HALT” instruction. After then, MCU wake-up from HALT mode, MCU system frequency is

already changed to the new setting frequency.

RCSEL2

RCSEL1

RCSEL0

Frequency of MCU system clock

0

0

0

256KHz

0

0

1

512KHz

0

1

0

1MHz

0

1

1

2MHz

1

#

#

4MHz

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