Information

CRC_CTRL field descriptions (continued)

Field Description

TCRC

Width of CRC protocol.

0 16-bit CRC protocol.

1 32-bit CRC protocol.

23–0

Reserved

This read-only field is reserved and always has the value zero.

31.3 Functional description

31.3.1 CRC initialization/re-initialization

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

data register.

After a completed CRC calculation, re-asserting the CTRL[WAS] bit and programming a

seed (whether the value is new or a previously used seed value) re-initialize 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. Non-contiguous bytes can lead to an

incorrect CRC computation.

31.3.2.1 16-bit CRC

Compute a 16-bit CRC with the following steps:

1. Clear the CTRL[TCRC] bit 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 the CTRL[WAS] bit to program the seed value.

Functional description

K20 Sub-Family Reference Manual, Rev. 6, Nov 2011

714 Freescale Semiconductor, Inc.