Chapter · SPI
Wider belts
Two, four and eight lines for flash and memory, the flash modes on an ESP32-S3, and what a wrong setting looks like.
- 11Dual SPI4 minDual SPI turns the two data wires round so both point the same way, and a byte takes four clocks instead of eight. The cost is talking and listening at once.
- 12Quad SPI4 minQuad SPI turns four pins into four data lines pointing the same way, so a byte takes two clocks instead of eight. It costs the two-way swap, and it costs a short silence between the address and the data.
- 13Octal and flash modes4 minThe letters on an ESP32 board menu, DIO, QIO and OPI, count the data lines between the chip and its flash or PSRAM, which are two, four and eight. More lines read faster, and the setting has to match what the module really contains.
- 14When it goes wrong4 minFour faults account for most SPI that misbehaves. Two peripherals answer at once, two ends disagree about the mode, the clock is faster than a part can follow, or a chip select is tied low. None of them raises an error, and each has a symptom of its own.
Start at 11 and read down — the order is the order things get easier in. Or take the one with your part in it; every article stands on its own, and links back to whatever it needs.