Processor communicates with the TM1638 using variation of SPI interface. The TM1638 board has just 3 control pins plus power and ground. The control pins are strobe, clock and data. Data is a bidirectional SPI pin, clock is SPI clock, strobe LOW selects the chip. There is special communication protocol. TM1638 listens only when strobe line is LOW. First byte send to TM1638 is a command. Then strobe should go HIGH. After that one can send arguments for the command (if present). During transfer of arguments strobe should be LOW.

The TM1637 board uses variation of I2C interface. However it is incompatible with standard I2C. Namely it has no address and bits are transmited starting from the lowest bit (opposite to I2C). Communication with TM1637 begins from I2C start condition. First byte send is a command, which may be followed by data. Like in proper I2C bytes are followed by acknowledgement bit. Transfer ends with I2C stop condition.

TM163x has 4 functions:

• activate/deactivate board and initialise display
• write a byte at specific address
• write bytes starting from specific address
• read buttons

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