Digital Electronics: Principles, Devices and Applications

596 Digital ElectronicsV CCI/O PinI/O PinI/O Pin10K10K10K10KI/O PinMicrocontrollerI/O PinI/O PinI/O Pin1K1K1KRow1Row2Row3Col1Col2 Col3 Col4I/O Pin1KRow4GNDFigure 14.29Connection of a 16-key matrix keypad with a microcontroller.whether any of the normally HIGH column lines are pulled LOW. If a column is driven LOW, then, bydetermining which row and column line is LOW, the key is identified and the routine correspondingto that key press is executed.14.6.4 Interfacing Seven-Segment DisplaysSeven-segment displays commonly contain LED segments arranged as a figure-of-eight pattern, withone common lead (anode or cathode) and seven individual leads for each segment. When the commonlead is the anode it is referred to as the common anode (CA), and when the common lead is the cathodeit is referred to as the common cathode (CC). Figure 14.30 shows one of the possible configurationsof interfacing a CC display with the microcontroller. The IC CD4511 is a BCD to seven-segmentdecoder/driver. The microcontroller feeds the BCD equivalent of the digit to be displayed to the 4511IC.Seven-segment displays can also be connected directly without the use of a BCD to seven-segmentdecoder. In this case the seven-segment code of the digit is generated by the microcontroller programitself. Figure 14.31 shows the direct circuit connection for CA display.If more than one display is to be used, the displays are time multiplexed. The human eye cannotdetect the blinking display if each display is relit every 10 ms or so. The 10 ms time is divided by thenumber of displays used to find the interval between updating each display. In the case of CC displays