SPI has no built-in error detection. How do you ensure data integrity?

SPI's shift-register design provides no ACK/NACK, no CRC, and no parity — a corrupted byte is silently accepted. This means error detection must be implemented at a higher layer, and the strategy depends on the device and application.

Read-back verification: After writing a configuration register, read it back and compare. This catches both SPI transmission errors and device-side failures. Many SPI devices (accelerometers, flash chips) support this pattern. The overhead is one extra transaction per write.

Application-layer CRC or checksum: For bulk data transfers (reading sensor FIFOs, flash pages), compute a CRC over the received data and compare it against a CRC provided by the device. Some SPI flash chips (Winbond W25Q series) include a CRC in their read responses. For devices that do not, the application protocol can add one.

Write-then-read pattern with known values: Before a critical transaction, send a "who am I" or "read device ID" command. If the response matches the expected value, the SPI link is functional. This is a common health-check pattern in initialization code.

Hardware considerations: At high SPI clock speeds (above 10-20 MHz), signal integrity becomes the dominant error source. Keep traces short (under 10 cm), add series termination resistors (22-33 ohm) on SCK and MOSI to reduce ringing, use ground planes, and avoid routing SPI traces near switching power supply inductors. Decoupling capacitors (100 nF) close to each slave's VDD pin are essential. If you see intermittent data corruption at high speeds, the first debugging step is to reduce the SPI clock frequency — if errors disappear, the problem is signal integrity, not firmware.