Codes and Code Converters

1. Codes andCode 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. Table 9.2 Standard ASCII codes Dec 0 16 32 48 64 80 96 112 Hex 0 1 2 3 4 5 6 7 0 0 NUL DLE blank 0 @ P p 1 1 SOH DC1 ! 1 A Q a q 2 2 STX DC2 " 2 B R b r 3 3 ETX DC3 # 3 C S c s 4 4 EOT DC4 $ 4 D T d t 5 5 ENQ NAK % 5 E U e u 6 6 ACK SYN & 6 F V f v 7 7 BEL ETB ' 7 G W g w 8 8 BS CAN ( 8 H X h x 9 9 HT EM ) 9 I Y i y 10 A LF SUB * : J Z j z 11 B VT ESC + ; K [ k { 12 C FF FS , < L \ l | 13 D CR GS - = M ] m } 14 E SO RS . > N ^ n ~ 15 F SI US / ? O _ o DEL Standard ASCII Codes

4. ASCII Codes

5. Definitions of ASCIIControl Characters

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

13. Binary-to-BCD Converter

14. I = 1110 E D C B A 1 4 bin2bcd.abl MODULE bin2bcd TITLE 'Binary to binary coded decimal' DECLARATIONS " INPUT PINS " I3..I0 PIN 11,7,6,5; " Switches S6 - 1..4 I = [I3..I0]; " 4-bit input vector " OUTPUT PINS " [E,D,C,B,A] PIN 5,4,3,2,1 ISTYPE 'com'; " LEDs 12..16 BCD = [E,D,C,B,A];

15. EQUATIONS @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 Gray Code 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)