Port 1: This is a dedicated I/O port occupying pins 1 to 8 of the device。 The pins are connected via internal pull-ups and Schmitt trigger input。 Pins that have 1s written to them are pulled high by the internal pull-ups and can be used as inputs; as inputs, pins that are externally pulled low will source current via the internal pull-ups。 The port also receives the low-order address byte during program memory verification。 Pins P1。0 and P1。1 could also function as external inputs for the third timer/counter i。e。:

(P1。0) T2 Timer/counter 2 external count input/clockout (P1。1)   T2EX   Timer/counter   2  reload/capture/direction

control

Port 2: This is a dual-purpose port occupying pins 21 to 28 of the device。 The specification is similar to that of port 1。 The port may be used to provide the high-order byte of the address bus for external program memory or external data memory that uses 16-bit addresses。 When accessing external data memory that uses 8-bit addresses, the port emits the contents of the P2 register。 Some port 2 pins receive the high-order address bits during EPROM programming and verification。

Port 3: This is a dual-purpose port occupying pins 10 to 17 of the device。 The specification is similar to that of port 1。 These pins, in addition to the I/O role, serve the special features of the 80C51 family B。

V。ACCELARATORS

A。CONVERTING ACCELERATIONS

Fig。 5 shows the axis orientation of the MMA7260QT。 The positive signs along x-, y-, and z-axis (with arrows indicated) define the direction that the sensor is accelerated to。 The outputs from the MMA7260QT are analog signals with maximal bandwidth response of 350Hz (x- and y-axis) and 150Hz (z-axis)。 For any axis with no applied acceleration, its output is equal to half the supply voltage (VDD)。 The output voltage increases from the half VDD level when the sensor is accelerated in the positive direction along its sensitive axis。 On the contrary, the signal output is below the half VDD level when the sensor is accelerated in negative direction (or decelerated) along its sensitive axis。

Figure 5。   Axis orientation of the MMA7260QT

For a typical VDD=3。3V application, the zero-acceleration output is 0。5×3。3=1。65V。 When the sensor is accelerated, the outputs of the sensitive axes deviate from 1。65V and the variation is according to the selected sensitivity S (mV/g, voltage per gravity) as shown in Table I For example, if 2g sensitivity is selected, its sensitivity is 600mV/g (g is gravity in the amount of 9。81m/s2) and the voltage within the sensitivity range changes linearly with the measured acceleration (Acc)。

Sensitivity can be selected with 2 logic inputs connected to pin g-Select 1 and g-Select 2。 The sensitivity can be changed at anytime during operation。 The g-select pins of the MMA7260QT can be configured with high (1) or low (0) status by microcontroller outputs, as shown in Table I。 The   g-select

pins can be left unconnected for applications only requiring  

1。5g selectivity。  

arcsin  CC z 

The Sleep Mode pin can be connected to a logic inputs  for  

mode switch。 Set this pin low to enable MMA7260QT in Sleep  

Mode that  will only consumed trickle current。  A high     logic

input at this pin will switch the sensor to normal operation mode。

B。TILT SENSING