While the ASCII code is widely used on personal computer and many
minicomputers, it is not the only coding format used on computers. One of the most commonly used coding schemes for mainframes is the Extended Binary Coded Decimal Interchange Code (EBCDIC). With EBCDIC, each byte (eight bits) is divided into two portions - zone portion and the digit portion. The bits in both the zone portion and the digit portion are assigned numeric values based upon the binary number system, forming the basis for a logical representation of data in storage. Numeric values are represented in EBCDIC with all zone bits “on” and the proper combination of bits in the digit portion of the byte “on” to represent the particular value. For example value 4 is represented in the following manner.
Z 1011001
J 0100001
The parity bit is put to use each time the computer processes a representation. The number of 1’s in the 6-bits set of a representation is compounded and is ascertained if they correspond to the parity bit placed on the left. If they correspond, the representation is accepted and processed, otherwise, an error signal is given by the computer meaning that there is something wrong with the computer circuitry. For example, suppose because of improper working of the computer circuit, Z is being mis-represented as 1011000. In the 6-bits of the mis-representation, there are two 1’s meaning that parity bit should be 0 whereas actually it is 1.
The above type of parity bit is known as the even parity bit since the number of 1’s in the 7-bits set for a representation is always even. Similarly, the odd parity check can be employed but the two checks are mutually exclusive, i.e., only one of them is performed.
INTEXT QUESTIONS
7. Convert the following numbers into decimal system:
(a) (1100001)
2
(b) (2315)
8
(c) (121A)
16
8. Convert the following from one number system to another number system.
(a) (572)
10
= ( )
8
(b) (A = 29)
16
= ( )
10
(c) (101101.01)
2
= ( )
10
(d) (3572)
8
= ( )
16
(e) (256)
8
= ( )
2