QSPI

Quad Serial Peripheral Interface (QSPI) is an extension of the Serial Peripheral Interface (SPI) standard that uses four data lines to transfer data between a host processor and an external device, typically flash memory. By employing four IO lines instead of a single data line, QSPI can achieve significantly higher data throughput in suitable hardware.

QSPI devices use four bidirectional data lines (commonly labeled IO0 through IO3) alongside the clock (SCK) and chip select (CS). Data can be transferred on multiple lines in parallel, and the protocol supports various modes, including quad I/O, where commands, addresses, and data may be transmitted over multiple lines. In operation, an instruction is issued, followed by an address phase and then a data phase; clocking follows the device's CPOL/CPHA requirements as with standard SPI.

QSPI is widely used for serial flash memory in embedded systems, boot devices for microcontrollers, and storage in consumer electronics. It provides higher sustained throughput than conventional SPI flash, enabling faster reads and shorter boot times. Its drawbacks include greater pin count, more complex controller logic, and the need for compatible flash devices and careful signal integrity at higher frequencies.

Related interfaces include SPI, dual-SPI, and octal-SPI. QSPI is sometimes referred to as Quad SPI, and many flash vendors market Quad SPI flash memory devices designed to operate in quad I/O modes.