(74LS47)BCD-to-Seven Decoder and 7 Segment Display Rajeev Varkey rcv110@psu.edu CENBD 452 Fall 2002

Components 8 input DIP Switch 8 pin 330 Ω SIP resistor network SN7447AN BCD-to-Seven Decoder Common Anode 7 segment Display

BCD-to-Seven Pins Pins D, C, B, and A is the BCD input. RBI – Ripple-Blanking Input. BI/RBO – Blanking Input or Ripple Blanking Output LT – Lamp-Test Input a – g represent segments on display RBI, BI, LT are Active Low

Hex-to-Seven Outputs *Outputs of decoder are open-collectors.

7 Segment Display Two Types Common Anode(CA) Common Cathode(CC)

Common Anode or Cathode? Common Cathode All LED Segments Share a Common Positive Terminal (VCC) Active Low Use Decoder 7447 All LED Segments Share a Common Negative Terminal (GND) Active High Use Decoder 7448

Performance and Cost Propagation delays Cost Turn-off and Turn-on time from A and RBI input = 100ns Cost 74LS47 - $0.99 LSD8151-10 - $1.49 DIP switch - $0.89 SIP Resistors – 4 x $0.26