Other Binary Code

In previous sections we introduced the most common types of binary-coded data found in digital computers. Other binary codes for decimal numbers and alphanumeric characters are sometimes used. Digital computers also employ other binary codes for special applications. A few additional binary codes encountered in digital computers are presented in this section.

Gray Code: Digital systems can process data in discrete form only. Many physical systems supply continuous output data. The data must be converted into digital form before they can be used by a digital computer. Continuous, or analog, information is converted into digital form by means of an analog-to-digital converter. The reflected binary or Gray code, shown in Table 3-5, is sometimes used for the converted digital data. The advantage of the Gray code over straight binary numbers is that the Gray code changes by only one bit as it sequences from one number to the next. In other words, the change from any number to the next in sequence is recognized by a change of only one bit from 0 to 1 or from 1 to 0. A typical application of the Gray code occurs when the analog data are represented by the continuous change of a shaft position. The shaft is partitioned into segments with each segment assigned a number. If adjacent segments are made to correspond to adjacent Gray code numbers, ambiguity is reduced when the shaft position is in the line that separates any two segments.

Gray code counters are sometimes used to provide the timing sequences that control the operations in a digital system. A Gray code counter is a counter whose flip-flops go through a sequence of states as specified in Table 3-5. Gray code counters remove the ambiguity during the change from one state of the counter to the next because only one bit can change during the state transition.

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