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e.g. The sequence of numbers below will convert to

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A W E E T E S T

21.3 DATA CHARACTERIZATION

21.3.1 Parity

•Parity - used to detect errors in data. A parity bit can be added to the data. For example older IBM PCs store data as bytes, with an extra bit for parity. This allows real-time error checking of memory.

•Parity can be even or odd.

•The odd parity bit is true if there are an odd number of bits on in a binary number. On the other hand the Even parity is set if there are an even number of true bits.

	data	parity
	bits	bit
e.g.
Odd Parity	10101110	1
	10111000	0
Even Parity:	00101010	0
	10111101	1

• Convert the decimal value below to a binary byte, and then determine the odd parity bit,

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21.3.2 Gray Code

•A scheme to send binary numbers, but encoded to be noise resistant.

•The concept is that as the binary number counts up or down, only one bit changes at a time. Thus making it easier to detect erroneous bit changes.

ASIDE: When the signal level in a wire rises or drops, it induces a magnetic pulse that excites a signal in other nearby lines. This phenomenon is known as ‘cross-talk’. This signal is often too small to be noticed, but several simultaneous changes, coupled with background noise could result in erroneous values.

e.g. GRAY CODE sequence	dec	gray code
	0	0000
	1	0001
	2	0011
	3	0010
	4	0110
	5	0111
	6	0101
	7	0100
	8	1100
	9	1101
	10	1111
	11	1110
	12	1010
	13	1011
	14	1001
	15	1000