The seventh bit was used as a parity bit, and the eighth as a "Word Mark".
(This calculation is called a parity check, and the redundant bit is called a parity bit). The second parity bit is chosen so that the sum of the ones in the last three information bits plus the second parity bit is even, and the third parity bit is chosen so that the sum of ones in the first, second, and fourth information bits and the last parity bit is even.
In practice, adding a parity bit to a two-bit code is not very efficient, but for longer codes adding a parity bit is reasonable.
For instance, computer and fax modems often communicate by sending eight-bit blocks, with one of the bits reserved as a parity bit.
The mouse uses a serial protocol to transmit the data, starting with a start bit, followed by 8 data bits, followed by a parity bit, and finally a stop bit.
The ASCII code is actually specified as a 7-bit code with 128 characters plus an extra bit designed as a parity bit that makes it an 8-bit code.
One of the bits was not accessible because it was a parity bit and another bit was the Word Mark (WM) which marked the beginning of instruction (reading up) and the end of a data field (reading down through memory).
Because digital computers use eight-bit bytes, the ASCII code is commonly embedded in an eight-bit field consisting of the seven information bits and a parity bit that is used for error-checking purposes or to represent special symbols.
The Xbee link ensures data coherency using a parity bit, and the receiver/Matlab handshake also ensures a correct data transfer.
The SIGNAL field includes a RATE and a LENGTH field, one reserved bit, a parity bit and 6 tail bits and is one OFDM symbol long.
To detect this, a parity bit was used to verify the correctness of each sequence.
