Convert between SPI mode number and CPOL/CPHA, see the clock idle state and sample edge, and check the equivalent Arduino, STM32 HAL, and Linux spidev names.
The mode number is the same standard across platforms: mode = (CPOL << 1) | CPHA. Use this table to match your library's naming to the CPOL/CPHA your peripheral's datasheet specifies.
| Mode | CPOL/CPHA | Arduino SPI | STM32 HAL | Linux spidev |
|---|---|---|---|---|
| 0 | 0 / 0 | SPI_MODE0 | POLARITY_LOW, PHASE_1EDGE | SPI_MODE_0 |
| 1 | 0 / 1 | SPI_MODE1 | POLARITY_LOW, PHASE_2EDGE | SPI_MODE_1 |
| 2 | 1 / 0 | SPI_MODE2 | POLARITY_HIGH, PHASE_1EDGE | SPI_MODE_2 |
| 3 | 1 / 1 | SPI_MODE3 | POLARITY_HIGH, PHASE_2EDGE | SPI_MODE_3 |
CPOL (Clock Polarity) sets the SPI clock idle level: 0 means idle low, 1 means idle high. CPHA (Clock Phase) sets which clock edge data is sampled on: 0 samples on the leading edge of each clock cycle, 1 samples on the trailing edge. The four combinations of CPOL and CPHA give the four SPI modes, numbered 0 through 3.
Check the peripheral's datasheet timing diagram or electrical characteristics section. Many datasheets state the mode number directly; others only show CPOL and CPHA, or a clock waveform with the data valid window marked. Match that waveform against the diagram above to identify CPOL and CPHA, then read off the mode number.
If CPOL is wrong, the clock idles at the wrong level and the very first bit can be missampled or shifted by one bit position. If CPHA is wrong, every bit is sampled on the wrong edge, which usually produces consistently garbled or shifted data rather than an intermittent failure, making a mode mismatch one of the first things worth checking when a new SPI device returns nonsense.
Mode 0 uses CPOL 0 and CPHA 0, so the clock idles low and data is sampled on the rising edge. Mode 3 uses CPOL 1 and CPHA 1, so the clock idles high and data is also sampled on the rising edge, just relative to a different idle level.
Check its datasheet for CPOL and CPHA values, an explicit mode number, or a clock timing diagram. If only a diagram is given, compare the clock idle level and the edge where data changes against the diagram on this page to identify the mode.
The underlying CPOL/CPHA electrical behavior is identical, and the mode numbering 0 to 3 is the same standard everywhere, but each platform names it differently in code, such as SPI_MODE0 on Arduino or SPI_POLARITY_LOW with SPI_PHASE_1EDGE on STM32 HAL.
Mode 0 (CPOL 0, CPHA 0) is the most common default across many microcontrollers, sensors, and SD cards, but always confirm against the specific device datasheet since several common parts use mode 1, 2, or 3.
Yes. Since mode equals CPOL shifted left by one bit combined with CPHA, CPOL is the mode number's upper bit and CPHA is its lower bit, which is exactly what the mode buttons on this page compute for you.