# Codes and Code Converters

## Presentation on theme: "Codes and Code Converters"— Presentation transcript:

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

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

Standard ASCII Codes Standard Table 9.2 ASCII codes Dec Hex @ P p ! A
16 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

ASCII Codes

Definitions of ASCII Control Characters

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

Binary-to-BCD Converter

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];

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)

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.

Steps to convert an 8-bit binary number to BCD

Example of converting hex E to BCD

A3 A2 A1 A0 C S3 S2 S1 S0

Binary-to-BCD Converter

Binary-to-BCD Converter

Other Binary Coded Decimal Representations

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

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

Gray codes eliminate errors
Binary Code

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]

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]

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

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