The FT232 USB-to-serial converter is one of the most commonly-used methods of adding USB functionality to small projects, but recently I found that these chips are capable of sending more than just serial signals. With some creative programming, individual output pins can be big-banged to emulate a clock, data, and chip select line to control SPI devices. This post shares some of the techniques I use to bit-bang SPI with FTDI devices, and some of the perks (and quirks) of using FTDI chips to bit-bang data from a USB port. Code examples are available on GitHub, and links to additional resources are at the bottom of this post. After the final build I created a slightly more polished “ftdiDDS.exe” program to control an AD9850 frequency synthesizer from the command line by bit-banging a FT-232, and code (and binaries) are also available on GitHub.”

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