Data Acquisition

character can still be interpreted as an ASCII value if required (in which case the eighth bit –the most significant bit is ignored).It is worth mentioning that the full hexadecimal range can in fact be transmitted over a 7-bitlink by representing each hexadecimal digit as its ASCII equivalent. Thus the hexadecimalnumber 8E would be represented as the two ASCII (hexadecimal) values 38 45 (‘8’ ‘E’). Thedisadvantage of this technique is that the amount of data to be transferred is almost doubled,and extra processing is needed at each end.ASCII (American Standard Code for Information Interchange) is the most commonly usedcode for encoding characters for data communications. It is a 7-bit code with only 2 7 = 128possible combinations of the seven binary digits (bits).Each of these 128 codes is assigned to a specific control code or character, as specified bythe these standards:• ANSI – X3.4• ISO – 646• CCITT alphabet #5An ASCII table records the bit value of every character defined by the code. There aremany different forms of the table, but they all contain the same basic information. The valuesin the table may be expressed in decimal (DEC), ranging from 0–127, or in binary (BIN),ranging from 0000000 to 1111111, or in hexadecimal (HEX) numbers, ranging from 00 to7F. (See Table 6.2 for examples of binary to hexadecimal conversions.)A condensed form of the table showing characters and control codes is presented in Table6.1. The control codes and their meanings are listed in Table 6.3.Table 6.1 shows the code for each character in hexadecimal and binary values. It takes theform of a matrix in which the MSB (most significant bits) are along the top and the LSB(least significant bits) are down the left-hand side. Table 6.1ASCII table