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W921C843

4-BIT MICROCONTROLLER

Winbond 

W921E840A/W921C840

• P6.0 to P6.3: Multi-function I/O pins (selected by P6IO register)

− Normal function I/O pins

− Special function I/O pins

P6IO register: (address = 012H, default data = 0H)

b3

b2

b1

b0

0: Normal I/O P6.0

1: Work as the data output pin of the WCLK pin

(WDATA)

0: Normal I/O P6.1

1: Work as the clock I/O pin of the WDATA pin

(WCLK)

0: Normal I/O P6.2

1: Work as the data input pin of the RCLK pin

(RDATA)

0: Normal I/O P6.3

1: Work as the clock I/O pin of the RDATA pin

(RCLK)

• PA.0 to PA.3: Normal function I/O pins only

• PB.0 to PB.3: Normal function I/O pins only

• PC.1 to PC.3: Normal function I/O pins only

• PD.0 to PD.1: Normal function I/O pins only

6.5.2 Pull High and Open Drain Control of I/O

Some of the above I/O ports can be controlled with pull-high resistor or open drain by programming

the special register.

All pull-high resistors of the following descriptions are 400KΩ under 3.0 voltage test condition. After

power-on reset the following special register will all reset to 0H.

• P4.0 to P4.3:

P4PH register: (address = 003H, default data = 0H)

b3

b2

b1

b0

0: P4.0 without pull-high resistor

1: P4.0 with pull-high resistor

0: P4.1 without pull-high resistor

1: P4.1 with pull-high resistor

0: P4.2 without pull-high resistor

1: P4.2 with pull-high resistor

0: P4.3 without pull-high resistor

1: P4.3 with pull-high resistor

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Publication Release Date: July 1999

Revision A3

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