Petition: Change Supply Secure Hardware SPI Pin Names

Hi Particle,

I’m excited about the new Supply Secure Hardware Portfolio, in particular the Photon 2 development kit.

I realize these products are already in various stages of completion, but I would like to petition Particle to replace the outdated terminology for SPI. In fact there is a already established recommendation from the Open Source Hardware Association that is supported by companies such as Texas Instruments and Sparkfun.

Here is the what the proposal calls for:

New Signal Names:

  • SDO – Serial Data Out. An output signal on a device where data is sent out to another SPI device.
  • SDI – Serial Data In. An input signal on a device where data is received from another SPI device.
  • CS – Chip Select. Activated by the controller to initiate communication with a given peripheral.
  • PICO (peripheral in / controller out). For devices that can be either a controller or a peripheral; the signal on which the device sends output when acting as the controller, and receives input when acting as the peripheral.
  • POCI (peripheral out / controller in). For devices that can be either a controller or a peripheral; the signal on which the device receives input when acting as the controller, and sends output when acting as the peripheral.
  • SDIO – Serial Data In/Out. A bi-directional serial signal.

Deprecated signal names:

  • MOSI – Master Out Slave In
  • MISO – Master In Slave Out
  • SS – Slave Select
  • MOMI Master Out Master In
  • SOSI Slave Out Slave In

Signal names unchanged:

  • SCK – Serial Clock. The clock for the bus generated by the controller.


We as hardware engineers and technologists can make our space more inclusive. In 2022, it is embarrassing that the wider tech industry is casually usually terms like “master” and “slave” in an era when we seek to make this space more welcoming.

At the moment, the Photon 2 still uses MOSI/MISO, but Particle has an opportunity to be a leader in this area by changing the “master slave” terminology in their products.

As an educator, I am aware of how stereotype threat can impact academic performance and learning so I already change the terms in slides and conversation.

Is this a change Particle can implement before release? If not, will it be on the product roadmap?


PS Similar terminology exists in other places like I2C as well as with “male female” wires. Unfortunately there doesn’t seem to be an industry consensus yet on I2C, but for wires I use “plug” and “socket” in class.


Hi Rob-

Thank you for bringing this up, I appreciate your thorough explanation! I cannot promise that Particle will change the names in the Photon 2 Development kit but I will bring it up with the Photon 2 team and make sure it is given full consideration.

Additionally in all future Particle tutorial videos I will make sure to refer to plug/socket instead of male/female. I agree that male/female is outdated.


Hi Colleen,

Thank you so much for your response! I am glad you will bring this up with the team, and I hope it can be reflected in Particle’s product line eventually. I am also very glad to hear about plug/socket change!


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