Original Publication Date: 1992-Jan-01
Included in the Prior Art Database: 2005-Mar-21
In adapter designs, there are often many control signals that are used between areas of the card that have no type of error detection (i.e., if an error occurs on the signal, the error will not be detected).
designs, there are often many control signals
that are used between areas of the card that have no type of error
detection (i.e., if an error occurs on the signal, the error will not
This type of situation
generates many problems. Failures in
these signals are not easily detected during manufacturing or in the
field. Testability of the entire adapter is decreased. If the
adapter runs without detecting this problem, corrupted information
will be processed by the adapter and passed on.
One of the
more common forms of protection for a set of signals
is to add an extra signal that contains parity information. The
extra signal is then used to determine if the information presented
on the other signals is valid. The signals included in the set
protected by a parity bit must all be related to each other in that
they are all synchronous (i.e., generated off the same clock).
disadvantages to using parity protection to cover all
the signals on an adapter card:
. Since the signals protected must be related to each other, a
separate parity signal (or signals) must be added to protect each set
of signals (or possibly an individual signal). This can add a large
number of extra signals to the adapter. As the number of signals on
an adapter increases, the failure rate and the complexity and length
of the diagnostic code also increase.
. Each device that has to generate parity will need more hardware
and each device that needs to check parity will need more hardware.
. Many vendor components do not support parity so other parts would
have to be added to generate and check parity for these vendor parts.
can be used to protect certain types of interfaces
without using parity. It can be used on any interface with duplex
communication (i.e., signal lines in both directions between
information is passed through unprotected signals, that
information is "echoed" back to the sender over a second set of
signal lines to insure that the information was received properly.
The sender would compare the echo to the signals it sent and, if an
error occurred, it can be narrowed down to one of...