SPI Modes & Chip-Select Rules · protocols

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What you'll learn

SPI is a family of device-specific serial contracts — CPOL, CPHA, chip-select timing, word format and shift order must agree.

Mode 0-3: CPOL (idle clock level) × CPHA (sample edge).
Chip select: active level, setup/hold time relative to clock.
Full-duplex: MOSI and MISO shift simultaneously.

Connection

Another serial timing contract — mode mismatch produces garbage data, not protocol errors.

Key diagram

Mode 0 prepares before it samples

Mode 0 prepares before it samples. Conventional CPOL=0, CPHA=0, with target-specific setup/hold and chip-select timing. This is an edge-role diagram, not a timing waveform.

Conventional CPOL=0, CPHA=0, with target-specific setup/hold and chip-select timing. This is an edge-role diagram, not a timing waveform.

Check yourself May the first data bit be launched for the first time at its rising sampling edge?

No. It must already satisfy setup before that sample; later bits are prepared on the opposite edge.

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