Information

31.3.1 CRC initialization/reinitialization

To enable the CRC calculation, the user must program the WAS, POLYNOMIAL, and

necessary parameters for transpose and CRC result inversion in the applicable registers.

Asserting CTRL[WAS] enables the programming of the seed value into the CRC data

After a completed CRC calculation, reasserting CTRL[WAS] and programming a seed,

whether the value is new or a previously used seed value, reinitialize the CRC module for

a new CRC computation. All other parameters must be set before programming the seed

value and subsequent data values.

31.3.2 CRC calculations

In 16-bit and 32-bit CRC modes, data values can be programmed 8 bits, 16 bits, or 32 bits

at a time, provided all bytes are contiguous. Noncontiguous bytes can lead to an incorrect

CRC computation.

31.3.2.1 16-bit CRC

To compute a 16-bit CRC:

1. Clear CTRL[TCRC] to enable 16-bit CRC mode.

2. Program the transpose and complement options in the CTRL register as required for

the CRC calculation. See Transpose feature and CRC result complement for details.

3. Write a 16-bit polynomial to the GPOLY[LOW] field. The GPOLY[HIGH] field is

not usable in 16-bit CRC mode.

4. Set CTRL[WAS] to program the seed value.

5. Write a 16-bit seed to CRC[LU:LL]. CRC[HU:HL] are not used.

6. Clear CTRL[WAS] to start writing data values.

7. Write data values into CRC[HU:HL:LU:LL]. A CRC is computed on every data

value write, and the intermediate CRC result is stored back into CRC[LU:LL].

8. When all values have been written, read the final CRC result from CRC[LU:LL].

Transpose and complement operations are performed on the fly while reading or writing

values. See Transpose feature and CRC result complement for details.

31.3.2.2 32-bit CRC

To compute a 32-bit CRC:

Functional description

K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012

706

Preliminary

Freescale Semiconductor, Inc.

General Business Information