Table of Contents
Advertisement
8. When all values have been written, read the final CRC result from CRC_DH1,
CRC_DH0, CRC_DL1 and CRC_DL0. The CRC is calculated bytewise, and two
clocks are required to complete one CRC calculation.
Transpose and complement operations are performed on the fly while reading or writing
values. See
Transpose feature
16.4.3 Transpose feature
By default, the transpose feature is not enabled. However, some CRC standards require
the input data and/or the final checksum to be transposed. The user software has the
option to configure each transpose operation separately, as desired by the CRC standard.
The data is transposed on the fly while being read or written.
Some protocols use little endian format for the data stream to calculate a CRC. In this
case, the transpose feature usefully flips the bits. This transpose option is one of the types
supported by the CRC module.
16.4.3.1 Types of transpose
The CRC module provides several types of transpose functions to flip the bits and/or
bytes, for both writing input data and reading the CRC result, separately using the
CTRL[TOT] or CTRL[TOTR] fields, according to the CRC calculation being used.
The following types of transpose functions are available for writing to and reading from
the CRC data register:
1. CTRL[TOT] or CTRL[TOTR] is 00.
No transposition occurs.
2. CTRL[TOT] or CTRL[TOTR] is 01.
Bits in a byte are transposed, while bytes are not transposed.
reg[7:0] becomes reg[0:7]
NXP Semiconductors
and
CRC result complement
MC9S08SU16 Reference Manual, Rev. 5, 4/2017
Chapter 16 Cyclic redundancy check (CRC)
for details.
253
Advertisement
Table of Contents
