I2C Inter-integrated circuit protocol uses clock and data lines to communicate short distances at slow speeds from a master to up to 128 addressable slave devices. A display is a slave device.
RS232 Recommended standard 232, a common serial protocol. Logic levels can be as high as +/-30V, a high level is negative, a low is positive.
RS422 Recommended standard 422, a more robust differential pair serial protocol.
TTL Transistor-transistor logic applied to serial protocol. Low level is 0V while high logic is 5V.
USB Universal Serial Bus protocol widely used in PCs.
