SyncMOS Technologies International, Inc.

SM8954A

8-Bits Micro-controller

With 16KB flash & 1KB RAM embedded

Specifications subject to change without notice contact your sales representatives for the most recent information.

Ver 2.1 SM8954A 08/2006

9

1.3 I/O Pin Configuration

The ports 1, 2 and 3 of standard 8051 have internal pull-up resistor, and port 0 has open-drain outputs. Each I/O pin

can be used independently as an input or an output. For I/O ports to be used as an input pin, the port bit latch must

contain a ‘1’ which turns off the output driver FET. Then for port 1, 2 and 3 port pin is pulled high by a weak internal

pull-up, and can be pulled low by an external source. The port 0 has open-drain outputs which means its pull-ups are

not active during normal port operation. Writing ‘1’ to the port 0 bit latch will causing bit floating so that it can be used as

a high-impedance input.

The port 4 used as GPIO will has the same function as port 1, 2 and 3.

2. Port 4 for PLCC or QFP package :

The bit addressable port 4 is available with PLCC or QFP package. The port 4 has only 4 pins and its port address is

located at 0D8H. The function of port 4 is the same as the function of port 1, port 2 and port 3.

Port4 (P4, $D8)

bit-7

bit-0

Unused

Unused

Unused

Unused

P4.3

P4.2

P4.1

P4.0

Read / Write:

-

-

-

-

R/W

R/W

R/W

R/W

Reset value:

*

*

*

*

1

1

1

1

The bit 3, bit 2, bit 1, bit 0 output the setting to pin P4.3, P4.2, P4.1, P4.0 respectively.

3.Watch Dog Timer

The Watch Dog Timer (WDT) is a 16-bit free-running counter that generate reset signal if the counter overflows. The

WDT is useful for systems which are susceptible to noise, power glitches, or electronics discharge which causing

software dead loop or runaway. The WDT function can help user software recover from abnormal software condition.

The WDT is different from Timer0, Timer1 and Timer2 of general 8052. To prevent a WDT reset can be done by

software periodically clearing the WDT counter. User should check WDR bit of SCONF register whenever un-predicted

reset happened

The purpose of the secure procedure is to prevent the WDTC value from being changed when system runaway.