eorex

EU1020

Feb.2009

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).

BASE1

BASE0

0

0

0

1

1

0

1

1

MCU clock selection

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

clock (Fsys) offers 4MHz, 2MHz, 1MHz, 500KHz or 250KHz 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 (Fsys)

0

0

0

250KHz

0

0

1

500KHz

0

1

0

1MHz

0

1

1

2MHz

1

#

#

4MHz (Fosc)

7/21