The basic ASCII character set has a total of 128 characters, with 96 printable characters, including common letters, numbers, punctuation, etc., and 32 control characters. Standard ASCII code encodes 7 binary characters, the corresponding ISO standard is ISO646 standard. The following table shows the basic ASCII character set and its encoding:
The memory of the ASCII code of letters and numbers is very simple. As long as we remember a letter or digital ASCII code (for example, a ASCII code of A is 65, 0 is 48), knowing the corresponding case of writing between the alphabets 32, can calculate the rest of the letter, the number ASCII code .
Although the standard ASCII code is 7-bit encoding, since the computer's basic processing unit is byte (1byte = 8bit), one ASCII character is still stored in one byte. One (highest bit) in each byte is typically maintained in the computer (can be used as a parity bit when data transmission).
Since the number of standard ASCII character set characters is limited, the requirements are often unable to meet in practical applications. To this end, the International Standardization Organization has developed ISO2022 standards, which specifies that the ASCII character set is expanded into a unified method of 8-bit code under the premise of maintaining ISO646 compatibility. ISO has successively developed a batch of expansion ASCII character sets for different regions, each expansion ASCII character set can be extended 128 characters, and these expansion characters are encoded with 8-bit code (ie, decimal 128 ~ 255) ), Called an extended ASCII code. The following table shows the most popular set of expansion ASCII character sets and encodings:
