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Seven Segment Display Interfacing With 8051. Seven Segment Display. Output Device Common Cathode Seven Segment Display Common Anode Seven Segment Display LED displays are – power-hungry (10ma per LED) – Pin-hungry (8 pins per 7-seg display)
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Seven Segment Display • Output Device • Common Cathode Seven Segment Display • Common Anode Seven Segment Display • LED displays are – power-hungry (10ma per LED) – Pin-hungry (8 pins per 7-seg display) • Limitation: only digits and few characters can be displayed • To view display from far distance
Common Cathode Code h g f e d c b a digit C.C.Hex-code 0 0 11 1 1 1 1 0 3f 0 0 00 0 1 1 0 1 06 0 1 01 1 0 1 1 2 5b 0 1 00 1 1 1 1 3 4F 0 1 10 0 1 1 0 4 66 0 1 10 1 1 0 1 5 6d 0 1 11 1 1 0 1 6 7d 0 0 00 0 1 1 1 7 07 0 1 11 1 1 1 1 8 7F 0 1 10 1 1 1 1 9 6F
Interfacing Multiple Seven segment LED • Direct Interfacing - one LED requires one PORT -Not feasible because only 4 ports in 8051 -All ports are engaged in display -More LEDs can not be connected • Software simplicity
Multiple LED Interfacing Using Latch with Each LED • Using Latch with Each LED • Hardware cost Increases-4 latch • No. of pins - 8+No.of LED • No Refreshing burden on software
Scanned 7-seg LED display • Scanned displays – Only one 7-seg display is enabled at a given time – Inputs a-h are connected together respectively • Total Port pins needed – 8 + # of digits – 8 + 4 for this figure
Scanned/Multiplex Seven Segment LED Interfacing • 74LS138 decoder is used to select digit • Latch is used to drive digit • Refreshing burden