Even

If the channel and communications equipment are configured to support Even Parity, the ‘receiving’ communications equipment expects the total numbers of bits that it receives in each transmission to comprise an even number.

The Parity bit is set to 1 if the number of 1s in the Data Bits is an odd number, so resulting in an even total (Parity bit + Data Bits).

The Parity bit is set to 0 if the number of 1s in the Data Bits is an even number, so retaining an even total.

In each case, the communications equipment checks that the sum total of the Data Bits including the Parity bit is an even number.

If the total number of bits including the Parity bit is even, it means that the data is complete and valid. The communications equipment will then pass the message to the ‘receiving’ application.

If the total number of bits including the Parity bit is odd, it means that the data has become corrupted during transit. The communications equipment will disregard the data and will not pass the message on to the ‘receiving’ application. If ClearSCADA is the ‘sending’ application and it does not receive a reply, it will time out the message. If repeated attempts to send the message continue to time out, ClearSCADA will generate an alarm.

However, in some instances, the communications equipment is not expected to reply even if the message was received correctly. In these situations, further diagnostics of the communications network and device are required.