(1) (
Resistor-
Transistor
Logic) The first type of digital circuit design, which used resistors at the inputs and a bipolar junction transistor (BJT) for switching. In the 1960s, transistors were expensive, and the RTL approach minimized their use. RTL was followed by diode-transistor logic and transistor-transistor logic (see
DTL and
TTL).
(2) (
Register
Transfer
Level) A high-level hardware description language (HDL) for defining digital circuits. The circuits are described as a collection of registers, Boolean equations, control logic such as "if-then-else" statements as well as complex event sequences; for example: "if the clock signal goes from 0 to 1, then load register A with the contents of register B plus register C." The most popular RTL languages are VHDL and Verilog. RTL specifications are turned into gate-level netlists. See
VHDL and
Verilog.
RTL Starts the Cycle
The digital chip circuit development cycle typically begins with designs turned into RTL.