LRC

A parity checking error control method that improves on the simple vertical redundancy check (VRC) by viewing data as a block, or data set. As shown in Table L-1, this approach is characterized in terms of the manner in which human beings add numbers, not only in columns, but also in rows across columns, as though the devices were viewing data set in a matrix format. This additional technique of checking the total bit values of the characters on a longitudinal (i.e., horizontal) basis employs the same parity (i.e., odd or even) as the vertical check technique in the example in Table L-1. LRC and VRC are easily and inexpensively implemented in devices employing asynchronous transmission. LRC adds a significant measure of reliability when used in conjunction with VRC, although compensating errors still can occur in non-adjacent characters.The LRC is sent as one or two extra characters, known as block check characters (BCCs), at the end of each data block. See also error control, parity check, and VRC.

Table L-1: Longitudinal Redundancy Check (LRC)

Bit/Value	C	O	N	T	R	O	L	Odd Parity
1	1	1	0	0	0	1	0	0
2	1	1	1	0	1	1	0	0
3	0	1	1	1	0	1	1	0
4	0	1	1	0	0	1	1	1
5	0	0	0	1	1	0	0	1
6	0	0	0	0	0	0	0	1
7	1	1	1	1	1	1	1	0
8 (Odd Parity)	0	0	1	0	0	0	0