QSPI (Quad - SPI) - Protocol and Use Cases

In this blog, we are going to learn fundamentals of Quad-SPI protocols, its applications and uses cases.
Lets get started -


          Figure #1 : QSPI Master/Slave Interface

Compared to traditional SPI two data lines (MOSI/MISO), QSPI supports four data lines (IO0/IO1/Io2/IO3) which makes it a faster protocol compared to traditional SPI interface.

Traditional SPI interface is mostly used to receive data from sensors or sending data to actuators or output devices.

QSPI is mostly used in memory interface where its four data lines are used to read, write and erase memory where the on chip memory is not sufficient and device needs an external memory.

Unlike normal SPI which uses separate input and output data lines (MISO and MOSI) , QSPI uses four bidirectional data lines which can be configured as input and output on the fly.





                        Figure #2 : QSPI Protocol Working


As you can see in the above diagram, the command is send first by the QSPI Master device. This command can be an instruction or an address. Followed by command few dummy cycles are sent  which allows configuring the IO directions by Master and Slave QSPI device (Input -> Output and Output -> Input). Then the data is written to the memory interfaced with QSPI followed by few more dummy cycles. The data from memory is read then.

QSPI Advantages :

1) Approximately four times throughput compared to normal SPI

2) Multiple devices can be connected to the same QSPI interface by making use of Chip Select.

3) Lower Pin Count compared to parallel memory interface which allows allows remaining on-chip GPIOs to be used or other purpose

4) Lower Pin count results in less PCB design complexity/cost

5) QSPI supports XIP which can help increase the code memory.


Thank !