Embedded Systems: An Integrated Approach by Pearson

SENSORS, ADCS AND ACTUATORS 109

a time, only one particular transistor is to be ON.  ese are PNP transistors and are

turned ON if a ‘0’ is applied to the bases.  is ‘0’ goes to the emitters of the transis-

tor which is connected to the common cathode of the segment LEDs, of a par-

ticular digit. At a time, Port 1 gives a ‘0’ only on one of its port lines. To understand

this clearly, observe Figure3.25.  e most signifi cant digit (or the left most digit of

the display) is activated by a ‘0’on pin P1.0. When this pin is cleared, P1.1 to Pi1.3

should be set. At the same time, the segment information for displaying the left

most digit should be placed on Port1. If Port 2 gives the data 77 H, the fi rst digit

displays ‘A’.

 is technique is ...