SECTION I-12: ASCII - American Standard Code for Information Interchange

All information in the computer must be represented by 0's and 1's, binary patterns must be assigned to letters and other characters. In the 1960's a standard representation called ASCII was established. The ASCII code assigns Binary patterns for numbers 0 to 9, all the letters of the English alphabet, both upper-case capital and lower case, and many control codes and punctuation marks. The advantage of this system i s that it is used by most computers, so that information can be shared among computers. The ACSII system uses a total of 7 bits to represent each code. Example 100 0001 is assigned to the upper-case letter "A" and 110 0001 is for the lower-case letter "a". A zero is placed in the most significant bit position to make it an 8-bit code. A completed list of ASCII codes is demonstrated below.

ascii-codes-list.jpg

The use of ASCII is not only standard for keyboards used in United States but also many other countries to provides a standard for printing and displaying characters by output devices such as printers and monitors. The pattern of ASCII codes was designed to allow for easy manipulation of ASCII data. Digits 0 to 9 are represented by ASCII codes 30 through 39. This enables a program to easily convert ASCII to decimal by masking off the "3" in the upper nibble. Also notice that there is a relationship between the uppercase and lowercase letters. The uppercase letters are represented by ACSII codes 41 through 5A and lowercase letters are represented by codes 61 through 7A. The only bit that is different between the uppercase "A" and lowercase "a" is bit 5. Therefore, conversion between uppercase and lowercase is as simple as changing bit 5 of the ASCII code.

 

 

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