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I just learned that Octospi can NOT be configured to be used as a standard SPI device as Octospi was designed to be used to interface with external memory devices.

The thing is, EEPROM ICs don't seem to advertise if the chip can interface with Octospi or not. Is there a way to tell?

As an example, I want to interface to CAT25512HU5I-GT3 by OnSemi. My team has interfaced with this device using standard SPI, but could Octospi be used since it is external memory? If not, any help finding a replacement would be greatly appriciated.

Thanks!

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  • \$\begingroup\$ Which device it is? If an MCU please give exact model, because, it depends on the exact model. OctoSpi may just be a fancy trademark name for a SPI bus with 8 data wires, the controller may allow using less wires, but it all boils down to what datasheet says the MCU is capable of. \$\endgroup\$
    – Justme
    Commented Mar 31, 2022 at 18:01
  • \$\begingroup\$ What is OctoSPI? Are you referring to the protocol? An EEPROM? Or a peripheral on an MCU? \$\endgroup\$
    – DKNguyen
    Commented Mar 31, 2022 at 18:03
  • \$\begingroup\$ I am programing the STM32L4S9AII6 by ST. \$\endgroup\$
    – Marshall Folkman
    Commented Mar 31, 2022 at 18:03
  • \$\begingroup\$ OctoSPI is a protocol. It is fairly new. \$\endgroup\$
    – Marshall Folkman
    Commented Mar 31, 2022 at 18:04
  • \$\begingroup\$ So you have read the MCU datasheet and reference manual about Octospi peripheral? \$\endgroup\$
    – Justme
    Commented Mar 31, 2022 at 18:04

2 Answers 2

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Quote from STM32 application note on Octospi (https://www.st.com/resource/en/application_note/an5050-octospi-interface-on-stm32-microcontrollers-stmicroelectronics.pdf)

"The OCTOSPI provides a flexible hardware interface, that enables the support of multiple hardware configurations: Single-SPI (traditional SPI), Dual-SPI, Quad-SPI, Dual-quad-SPI and Octo-SPI"

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  • \$\begingroup\$ So the octoSPI is not a protocol but configurable module in MCU. @michae \$\endgroup\$
    – user263983
    Commented Mar 31, 2022 at 18:30
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To find out if your EEPROM chip supports octoSPI, go to its datasheet and count the number of data pins used for the SPI connection. If there's 8 then it can do octospi, if theres 4 it can do quadspi. Quad and OctoSPI are usually "half-duplex" which means the same set of pins are used to send and receive data and only one of these operations can happen at once. Normal SPI (transmit only 1 bit at a time) is usually full-duplex which means it has separate wires for sending and receiving, and can do both at the same time. It has 2 wires for that, called SI and SO for "Serial in" and "serial out".

I would not recommend octoSPI, as Ive not seen many EEPROM parts with the correct pin arrangement. I would either use QuadSPI chip, or if you really need speed, use the Flexible External Memory Controller on your STM32 with a proper address and data bus.

If your EEPROM is only 64KB, you probably will not need anything faster than normal SPI as it would take approximately 25ms to completely read the whole EEPROM (512Kb/20MHz = 25ms)

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