FXPS7115D4 datasheet(25/72 Pages) NXP

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NXP Semiconductors

FXPS7115D4

Digital absolute pressure sensor, 40 kPa to 115 kPa

FXPS7115D4

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Product data sheet

Rev. 3 — 5 December 2019

25 / 72

Table 27. Reserved command response message bit field descriptions

Bit field

Definition

Command echo

Reserved command echo. Undefined

Data

Response data. Undefined

CRC[7:0]

8-bit CRC

7.5.4 Error checking

7.5.4.1 Default 8-bit CRC

7.5.4.1.1 Command error checking

The device calculates an 8-bit CRC on the entire 32 bits of each command. Message

data is entered into the CRC calculator MSB first, consistent with the transmission

order of the message. If the calculated CRC does not match the transmitted CRC, the

command is ignored and the device responds with the SPI error response.

The CRC decoding procedure is as follows:

1. A seed value is preset into the LSB of the shift register.

2. Using a serial CRC calculation method, the receiver rotates the received message

and CRC into the LSB of the shift register in the order received (MSB first).

3. When the calculation on the last bit of the CRC is rotated into the shift register, the

shift register contains the CRC check result.

4. If the shift register contains all zeros, the CRC is correct.

5. If the shift register contains a value other than zero, the CRC is incorrect.

The CRC polynomial and seed are shown in Table 28.

Table 28. SPI Command Message CRC

SPICRCSEED[3:0]

Default Polynomial

Default non-direct Seed

0000

x8+ x5+ x3+ x2+ x + 1

1111 1111

non-zero

x8+ x5+ x3+ x2+ x + 1

1111 SPICRCSEED[3:0]

7.5.4.1.2 Response error checking

The device calculates a CRC on the entire 32 bits of each response. Message data is

entered into the CRC calculator MSB first, consistent with the transmission order of the

message.

The CRC encoding procedure is as follows:

1. A seed value is preset into the LSB of the shift register.

2. Using a serial CRC calculation method, the transmitter rotates the transmitted

message and CRC into the LSB of the shift register (MSB first).

3. Following the transmitted message, the transmitter feeds 8 zeros into the shift

4. When the last zero is fed into the input adder, the shift register contains the CRC.

5. The CRC is transmitted.

The CRC polynomial and seed are shown in Table 29.

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