1. Codes and Code Converters
Lecture L6.12
Section 6.5
Section 9.5

2. Codes and Code Converters
ASCII
Binary-to-BCD Converters
Gray Code
Bar Codes

3. Standard ASCII Codes Standard Table 9.2 ASCII codes Dec Hex @ P p ! A16 32 48 64 80 96
112
Hex 1 2 3 4 5 6 7
NUL
DLE
blank @ P p
SOH
DC1 ! A Q a q
STX
DC2
" B R b r
ETX
DC3 # C S c s
EOT
DC4 $ D T d t
ENQ
NAK % E U e u
ACK
SYN
& F V f v
BEL
ETB ' G W g w 8 BS
CAN ( H X h x 9 HT EM ) I Y i y 10 LF
SUB * : J Z j z 11 VT
ESC + ; K [ k { 12 FF FS ,
< L \ l | 13 CR GS - = M ] m } 14 SO RS .
> N ^ n ~ 15 SI US / ? O _ o
DEL

4. ASCII Codes

5. Definitions of ASCII Control Characters

12. Codes and Code Converters
ASCII
Binary-to-BCD Converters
Gray Code
Bar Codes

13. Binary-to-BCD Converter

14. bin2bcd.abl E D C B A I = 1110 1 4 MODULE bin2bcd
MODULE bin2bcd
TITLE 'Binary to binary coded decimal'
DECLARATIONS
" INPUT PINS "
I3..I0 PIN 11,7,6,5; " Switches S
I = [I3..I0]; " 4-bit input vector
" OUTPUT PINS "
[E,D,C,B,A] PIN 5,4,3,2,1 ISTYPE 'com'; " LEDs
BCD = [E,D,C,B,A];

15. bin2bcd.abl (cont’d) EQUATIONS @radix 16; " Identify the Hex Base
@radix 16; " Identify the Hex Base
truth_table ( I -> BCD ) " Binary to BCD Code Converter
0 -> 00;
1 -> 01;
2 -> 02;
3 -> 03;
4 -> 04;
5 -> 05;
6 -> 06;
7 -> 07;
8 -> 08;
9 -> 09;
0A -> 10;
0B -> 11;
0C -> 12;
0D -> 13;
0E -> 14;
0F -> 15;
END bin2bcd
bin2bcd.abl (cont’d)

16. Shift and Add-3 Algorithm
1.      Shift the binary number left one bit.
2.      If 8 shifts have taken place, the BCD number is in the
Hundreds, Tens, and Units column.
3.      If the binary value in any of the BCD columns is 5 or greater,
add 3 to that value in that BCD column.
4.      Go to 1.

17. Steps to convert an 8-bit binary number to BCD

18. Example of converting hex E to BCD

19. Truth table for Add-3 Module
A3 A2 A1 A0 C
S3 S2 S1 S0

20. Binary-to-BCD
Converter

21. Binary-to-BCD
Converter

22. Other Binary Coded Decimal Representations

23. Codes and Code Converters
ASCII
Binary-to-BCD Converters
Gray Code
Bar Codes

24. Gray Code Note that the least significant bit
that can be changed without
repeating a value is the bit
that is changed

25. Gray codes eliminate errors
Binary Code

26. Gray Code Conversion Gray Code Decimal equivalent G_in = [G2..0];
G_out = [B2..0];
000 0
001 1
011 2
010 3
110 4
111 5
101 6
100 7
Truth_table (G_in => G_Out)
Fill in this TRUTH_TABLE
Command so as to convert
the Gray code input, [G2..0],
to the binary output, [B2..0]

27. Gray Code Conversion Gray Code Decimal equivalent G_in = [G2..0];
G_out = [B2..0];
000 0
001 1
011 2
010 3
110 4
111 5
101 6
100 7
Truth_table (G_in => G_Out)
0 -> 0; 1 -> 1;
3 -> 2; 2 -> 3;
6 -> 4; 7 -> 5;
5 -> 6; 4 -> 7;
Fill in this TRUTH_TABLE
Command so as to convert
the Gray code input, [G2..0],
to the binary output, [B2..0]

28. Codes and Code Converters
ASCII
Binary-to-BCD Converters
Gray Code
Bar Codes

29. Code 39 Bar Code A B C D 3-of-9 bars are WIDE bars
(Bars can be black or white)