A COMBINED PARITY AND STUFFING BIT FOR AN ASYNCHRONOUS SERIAL PROTOCOL CONTROLLER

Bit stuffing is used in asynchronous serial pro- atier each n (e.g., 5) bits of the same value in the tocols with relatively long messages (e.g., CAN pro- transmitter, while the receiver uses the transition tocol) and thus a need exists to supply the receiver and then deletes the artificially-inserted bit. The use enough transitions for synchronization. The imple- of bit-stuffing decreases the throughput of the serial mentation is to add an artificial, opposite-value bit line, and also adds logic for bit insertion/deletion.

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MOTOROLA Technical Developments Volume 22 June 1994

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A COMBINED PARITY AND STUFFING BIT FOR AN ASYNCHRONOUS SERIAL PROTOCOL CONTROLLER

by Ben-Arie Yoran, Rosen Benjamin and Saper Alexandre

  Bit stuffing is used in asynchronous serial pro- atier each n (e.g., 5) bits of the same value in the tocols with relatively long messages (e.g., CAN pro- transmitter, while the receiver uses the transition tocol) and thus a need exists to supply the receiver and then deletes the artificially-inserted bit. The use enough transitions for synchronization. The imple- of bit-stuffing decreases the throughput of the serial mentation is to add an artificial, opposite-value bit line, and also adds logic for bit insertion/deletion.

1234 5s 12 34 5s

internal

Clock

stuffing

S - Stuffed bit

                              Figure 1 Bit-stuffing PARITY MECHANISM systems), in such a way that the number of '1' bits in a message is complemented to an even number (i.e., A parity bit is used in serial communication to even parity), or an odd number (i.e., an odd parity). assure, up to a certain level of confidence, that the Obviously, the use of a parity bit decreases the data is error-free. This is usually done by inserting a throughput ofthe serial line.
parity bit after a number of bits (usually 8, in UART

St 1 2 3 4 5 6 7 8 P St

Internal Clock

message with even parity

message with odd parity

St Start or Stop bit P - Parity bit

Figure 2 Parity bit

The idea of this invention is to combine both If (Data-Byte = 00000000) THEN...