Hardware serial bus types

I2C:

• 2 lines: SCL (serial clock), SDA (serial data)
• default is high, pulled low for 0
• clock rising edge determines bit boundaries

SPI

• two lines for sending/receiving data – full duplex
• 4 lines: MISO, MOSI, SCK, CS

UART

• 2 lines: Rx, Tx
• asynchronous – no clock line
• but timing-sensitive: both devices know baud rate (transmission rate) ahead of time, and number of bits per message