MCP2517FD datasheet(70/98 Pages) MICROCHIP

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MCP2517FD

DS20005688B-page 70

 2017-2018 Microchip Technology Inc.

4.3

SPI Commands with CRC

In order to detect or avoid bit errors during SPI commu-

nication, SPI commands with CRC are available.

4.3.1

CRC CALCULATION

In parallel with the SPI shift register, the CRC is calcu-

lated, see Figure 4-7.

When nCS is asserted, the CRC calculator is reset to

0xFFFF.

The result of the CRC calculation is available after the

Data section of a CRC command. The result of the

CRC calculation is written to the CRC register in case

a CRC mismatch is detected. In case of a CRC mis-

match, CRC.CRCERRIF is set.

The MCP2517FD uses the following generator polyno-

mial: CRC-16/USB (0x8005). CRC-16 detects all sin-

gle and double-bit errors, all errors with an odd

number of bits, all burst errors of length 16 or less, and

most errors for longer bursts. This allows an excellent

detection of SPI communication errors that can hap-

pen in the system, and heavily reduces the risk of

miscommunication, even under noisy environments.

The maximum number of data bits is used while read-

ing and writing TX or RX Message Objects. A RX Mes-

sage Object with 64 Bytes of data + 12 Bytes ID and

Time Stamp contains 76 Bytes or 608 bits. In compari-

son, USB data packets contain up to 1024 bits. CRC-

16 has a Hamming Distance of 4 up to 1024 bits.

FIGURE 4-7:

CRC CALCULATION

SPI Shift Register

CRC Calculator

SCK

SDI

CRC Result

nCS

SDO

SDI

SDO

Reset

Safe

CRC command:

End of Data section

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