W921C880 查看數據表（PDF） - Winbond

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W921C880

4-BIT MICROCONTROLLER

Winbond 

W921E880A/W921C880

6.3 Internal Oscillator Circuit

There are dual clocks in this chip, one is a high speed clock, the other a low speed clock. The block

diagram is shown below:

f TM0

TM0

f SYS1

MUX0

f SYS0

MUX0

SYSCCR.0

TM1

f TM1

MUX1

TM2

f TM2

MUX2

TM3

f TM3

MUX3

11-bit

Prescaler

5-bit

Prescaler

f SYS System Clock f OSC

(1/4)

f1

f2

SYSCCR.3

*

2-bit Scaler

(1/4)

OSCI

f H Crystal Type or

RC Type

OSCO

f L 1-bit

Scaler

(1/2)

Enable (SYSCCR.1)

XT

Crystal Type

XT

Enable (SYSCCR.2)

* Default: cystal type, f1=fH, f2=fL (refer to 6.14 INI register)

The format of the system clock control reg. (SYSCCR) is shown below:

SYSCCR REG: ( ADDRESS = 000H, Default data = 0H)

b3

b2

b1

b0

0 : f TM0 = fsys0

1 : f TM0 = fsys1

0 : f H enable

1 : f H disable

0 : f L enable

1 : f L disable

0 : fosc = f 1

1 : fosc = f 2

The W921E880A/W921C880 provides a crystal or RC oscillation circuit selected by bit0 of the INI

register (refer to 6.14 INITIAL CONDITION Section) to generate the system clock through external

connections. If a crystal oscillator is used, a crystal or ceramic resonator must be connected to OSCI

and OSCO , and the capacitor must be connected if an accurate frequency is needed. The oscillator

configuration is shown as follows.

OSCI

or

OSCI

OSCO

OSCO

Crystal Type

RC Type

- 13 -

Publication Release Date: July 1999

Revision A3

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