TTL stands for Transistor-Transistor Logic, a serial communication commonly found in UART (universally asynchronous receiver/transmitter) transmission method, a method seen in most microcontrollers these days.(TTL) is a logic family built from bipolar junction transistors. Its name signifies that transistors perform both the logic function (the first "transistor") and the amplifying function (the second "transistor"), as opposed to resistor–transistor logic (RTL) or diode–transistor logic (DTL).