mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 628

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

Functional description
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.
28.3.3.1 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.
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1. CTRL[TOT] or CTRL[TOTR] is 00
2. CTRL[TOT] or CTRL[TOTR] is 01
3. CTRL[TOT] or CTRL[TOTR] is 10
4. CTRL[TOT] or CTRL[TOTR] is 11
No transposition occurs.
Bits in a byte are transposed, while bytes are not transposed.
reg[31:0] becomes {reg[24:31], reg[16:23], reg[8:15], reg[0:7]}
Both bits in bytes and bytes are transposed.
reg[31:0] becomes = {reg[0:7], reg[8:15],reg[16:23], reg[24:31]}
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MCF51JF128 Reference Manual, Rev. 2, 03/2011
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Figure 28-5. Transpose type 01
Figure 28-6. Transpose type 10
Preliminary
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Freescale Semiconductor, Inc.
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