Data In
Q D
Q D
Q D
Q D
Q D
Q D
Q D
Q D
Q D
Q D
Bit
15
Bit
12
Bit
11
Bit
10
Bit
6
Bit
5
Bit
4
Bit
3
Bit
1
Bit
0
Shift Clock
Cyclic Redundancy Check (CRC) Module Introduction
428
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
CRC Module
15.1 Cyclic Redundancy Check (CRC) Module Introduction
The CRC module produces a signature for a given sequence of data values. The signature is generated
through a feedback path from data bits 0, 4, 11, and 15 (see
). The CRC signature is based on
the polynomial given in the CRC-CCITT-BR polynomial (see
) .
f(x) = x
16
+ x
12
+ x
5
+1
(10)
Figure 15-1. LFSR Implementation of CRC-CCITT Standard, Bit 0 is the MSB of the Result
Identical input data sequences result in identical signatures when the CRC is initialized with a fixed seed
value, whereas different sequences of input data, in general, result in different signatures.
15.2 CRC Standard and Bit Order
The definitions of the various CRC standards were done in the era of main frame computers, and by
convention bit 0 was treated as the MSB. Today, as in most microcontrollers such as the MSP430, bit 0
normally denotes the LSB. In
, the bit convention shown is as given in the original standards
(bit 0 is the MSB). The fact that bit 0 is treated for some as LSB, and for others as MSB, continues to
cause confusion. The CRC16 module therefore provides a bit reversed register pair for CRC16 operations
to support both conventions.