King Billion Electronics Co., Ltd.

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HE89C21

HE80000 SERIES

January 20, 2003

8

V1.0E

SXI

SXO

33p

33p

32768Hz

If the dual clock mode is used, the LCD display, Timer1 and Timer Base will derive its clock source from

slow clock while the other blocks will operate with the fast clock.

9. General Purpose I/O

There are two dedicated general purpose I/O port, PRTC, PRTD. All the I/O Ports are bi-directional and

of non- tri-state output structure. The output has weak sourcing (50 µA) and stronger sinking (1 mA)

capability and each can be configured as push-pull or open-drain output structure individually by mask

option. The input port has built-in Schmidt trigger to prevent it from chattering. The hysteresis level of

Schmidt trigger is 1/3*VDD.

MO_?PP[...]

Output Structure

0

Open-drain output

1

Push-pull output

When the I/O port is used as input, the weakly high sourcing PMOS can be used as pull-up. Open drain

can be used if the pull-up is not required and let the external driver to drive the pin. Please note that a

floating pad could cause more power consumption since the noise could interfere with the circuit and

cause the input to toggle. A ‘1’ needs to be written to port first before reading the input data from the I/O

pin, otherwise, the pin will always be stuck at ‘0’. If the PMOS is used as pull-up, care should be taken to

avoid the constant power drain by DC path between pull-up and external circuit.

The initial state of most I/O ports is ‘1’ with one exception. The initial state of PRTD[2..0] is determined

by mask option MO_IH[2..0].

PRTD

Bit7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Reset

1

1

1

1

1

MO_IH2 MO_IH1 MO_IH0

MO_IH[2..0] Initial State of PRTD[2..0]

0

0

1

1