Serial interface. Allows ZX Spectrum to communicate with external peripherals and PC, through the most popular communication interfaces used in automation: UART (RS-232), SPI, I2C, and USB.
The device is configured by entering commands using a simple BASIC program on ZX Spectrum. While writing the program, there was some space left in the microcontroller's memory, so I placed an easter egg there. Do you know what movie this is from?
More info:
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