1. Dept. of Electrical and Computer Eng., NCTU
Lab 6. BCD Adder
Presenter: Chun-Hsien Ko
Contributors: Chung-Ting Jiang and Lin-Kai Chiu
Dept. of Electrical and Computer Eng., NCTU

2. Dept. of Electrical and Computer Eng., NCTU
Outlines
Binary and Decimal
BCD Adder and Decoder
4-bit Binary Full Adder (7483)
BCD Adder
Combinational Logic of BCD Decoder
7-segment Decoder
BCD-to-7-Segment Decoders (7447)
7-Segment LED
LAB 4: BCD Adder
Dept. of Electrical and Computer Eng., NCTU

3. Dept. of Electrical and Computer Eng., NCTU
Binary
4-bit binary digits can represent 16 different numbers (0~15)
Easy to compute in digital circuit
0x00, 0x01, …, 0x09, 0x0A, 0x0B, … ,0x0F
Binary-Coded Decimal (BCD)
A decimal digit can represent 10 different numbers (0~9)
Using 4-bit binary digits to represent a decimal digit
Familiar to most people
Only use 0x00 ~ 0x09 in 4-bit digits
Dept. of Electrical and Computer Eng., NCTU

4. Dept. of Electrical and Computer Eng., NCTU
Two 4-bit binary inputs:
A (A4;A3;A2;A1) and B (B4;B3;B2;B1)
Input 0≦A, B ≦9 → Output 0≦A+B ≦18
If A+B = 0~9
Output Carry = 0,Sum = A+B
If A+B = 10~18
Output Carry = 1, Sum = A+B+6
Why?
0x0A = (1010)2 = (10)10
(10000)2 – (01010)2 = (00110)2
Dept. of Electrical and Computer Eng., NCTU

5. Dept. of Electrical and Computer Eng., NCTU

6. BCD-to-7-Segment Decoders Dept. of Electrical and Computer Eng., NCTU
4-bit Binary Full Adder
BCD Adder
Combinational logic
BCD-to-7-Segment Decoders
Dept. of Electrical and Computer Eng., NCTU

7. Dept. of Electrical and Computer Eng., NCTU
4-bit Adder: 74LS83
No C0 in this Lab Pin 13 connect to GND
Dept. of Electrical and Computer Eng., NCTU

8. Dept. of Electrical and Computer Eng., NCTU
Combinational Logic of BCD Decoder
T8T4 + T8T2 + K
Add 6 or not (0110)
Dept. of Electrical and Computer Eng., NCTU

9. Dept. of Electrical and Computer Eng., NCTU
7-segment LED Display
Common anode pin ‘A’ and ‘k’ connect to VCC
LED illuminate when its input pin is low
Therefore, we need to decode the number for display with the 7-segment display
For example, if we want to show ‘1’, we need to input [ ] in term of [a b c d e f g dp]
Reference
Dept. of Electrical and Computer Eng., NCTU

10. Dept. of Electrical and Computer Eng., NCTU
BCD-to-7-Segment Decoders (7447)
Don’t care
N = 8*A+4*B+2*C+D
= (A;B;C;D)2
Dept. of Electrical and Computer Eng., NCTU

11. Dept. of Electrical and Computer Eng., NCTU
7-segment LED Display
330Ω(橘橘棕)
Dept. of Electrical and Computer Eng., NCTU

12. Dept. of Electrical and Computer Eng., NCTU
Dept. of Electrical and Computer Eng., NCTU

13. Dept. of Electrical and Computer Eng., NCTU
Lab 4: BCD Adder
Dept. of Electrical and Computer Eng., NCTU