How Can I Best Control the Bitrate of an SPI Master When I’m Working with Slower SPI Devices?

Question from the Customer:

I have been using the Aardvark I2C/SPI Host Adapter for many projects. Right now, I have a new project where I’ll be using the Aardvark adapter in SPI master mode. As I understand it, the slowest clock rate I can use in master mode is 125 kHz. However, for this project, I need a much slower bitrate, about 50 kHz. Is where a way I can slow down the Aardvark adapter (or another adapter) to communicate with slower SPI devices?

Response from Technical Support:

Thanks for your question! For your project, we recommend the Promira Serial Platform, which can be configured to the speed for the system requirement of your project.  As you noted, the bitrates that the Aardvark SPI master supports is 125 kHz to 8 MHz, which cannot be changed.  The Cheetah SPI Host Adapter also operates at higher speeds, 100 kHz to 40+ MHz. The clock rate of the Promira platform is much more flexible. As an SPI master, the Promira platfrom can operate at bitrates from 31 kHz to 80 MHz. As an SPI slave, the bitrate can range from 31 kHz to 20 MHz.

For more details about SPI bitrates and timing, please refer to the sections SPI Signaling Characteristics and SPI AC Characteristics of the Promira Serial Platform User Manual.

 Promira Serial Platform

Figure 1: Promira Serial Platform

You may find the Promira platform very useful for future projects – it provides a number of advantages over the Aardvark and Cheetah adapters, including:

  • Integrated level shifting from 0.9-3.3V (5V tolerant)
  • High-speed USB connectivity - provides high performance and convenience for benchtop programming, testing, and emulation
  • Ethernet connectivity - convenient for benchtop work, and enables remote control for your automation needs over long distances
  • More target power - provides a total of 200 mA to target devices
  • Scalability - SPI and I2C Active applications allow you to upgrade your Promira platform as needed; new applications will be released on a ongoing basis.

The following table provides a quick comparison between the levels of the Promira I2C and SPI Active Level applications, as well the Aardvark and Cheetah adapters.

 Compare the features of the Promira and the I2C/SPI Active Applications, and the Cheetah and Aardvark host adapters.

Additional resources that you may find helpful:

We hope this answers your questions. If you have other questions about our host adapters or other Total Phase products, feel free to email us at, or if you already own one of our devices and have a technical question, please submit a request for technical support.

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