Embedded Systems Design, 2nd Edition

82 Embedded systems design

processor, such as an error. Note that parity does not allow the

error to be corrected nor does it protect from all multiple bit

failures such as two set or cleared bits failing together. In addition

it requires a parity controller to calculate the value of the parity bit

on write cycles and calculate and compare on read cycles. This

additional work can slow down memory access and thus the

processor performance.

1 1 1 1 1

1

1 1 1

1 1 1 0 0

1

1 1 1

Ei

g

ht ones = Even = set parity

Six ones = Even = set parity

FAULT

1 1 1 1 1

1

1 1 1

1 1 1 1 0

1

1 1 1

Ei

g

ht ones = Even = set parity

Seven ones = Odd = clear parit

y

FAULT

Parity error

Parity correct ...