C8051F850-C-GM Datasheet, PDF (153/328 Pages) Silicon Laboratories – Low-Cost 8-bit MCU Family with up to 8 kB of Flash

18.2. Preparing for a CRC Calculation
To prepare CRC0 for a CRC calculation, software should set the initial value of the result. The polynomial
used for the CRC computation is 0x1021. The CRC0 result may be initialized to one of two values: 0x0000
or 0xFFFF. The following steps can be used to initialize CRC0.
1. Select the initial result value (Set CRCVAL to 0 for 0x0000 or 1 for 0xFFFF).
2. Set the result to its initial value (Write 1 to CRCINIT).
18.3. Performing a CRC Calculation
Once CRC0 is initialized, the input data stream is sequentially written to CRC0IN, one byte at a time. The
CRC0 result is automatically updated after each byte is written. The CRC engine may also be configured to
automatically perform a CRC on one or more 256 byte blocks read from flash. The following steps can be
used to automatically perform a CRC on flash memory.
1. Prepare CRC0 for a CRC calculation as shown above.
2. Write the index of the starting page to CRC0AUTO.
3. Set the AUTOEN bit to 1 in CRC0AUTO.
4. Write the number of 256 byte blocks to perform in the CRC calculation to CRCCNT.
5. Write any value to CRC0CN (or OR its contents with 0x00) to initiate the CRC calculation. The
CPU will not execute code any additional code until the CRC operation completes. See the note in
the CRC0CN register definition for more information on how to properly initiate a CRC calculation.
6. Clear the AUTOEN bit in CRC0AUTO.
7. Read the CRC result.
18.4. Accessing the CRC0 Result
The internal CRC0 result is 16 bits. The CRCPNT bits select the byte that is targeted by read and write
operations on CRC0DAT and increment after each read or write. The calculation result will remain in the
internal CR0 result register until it is set, overwritten, or additional data is written to CRC0IN.
18.5. CRC0 Bit Reverse Feature
CRC0 includes hardware to reverse the bit order of each bit in a byte as shown in Figure 18.2. Each byte
of data written to CRC0FLIP is read back bit reversed. For example, if 0xC0 is written to CRC0FLIP, the
data read back is 0x03. Bit reversal is a useful mathematical function used in algorithms such as the FFT.
CRC0FLIP
(write)
CRC0FLIP
(read)
Figure 18.2. Bit Reversal
Rev. 1.0
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