1. (74LS47)BCD-to-Seven Decoder and 7 Segment Display
Rajeev Varkey
CENBD 452 Fall 2002

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

3. 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

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

5. 7 Segment Display
Two Types
Common Anode(CA)
Common Cathode(CC)

6. 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

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