Multiplexers and demultiplexers¶
Laboratory Class 02 - 22 September 2021¶
Topics¶
Hardware and software architectures:
combinatorial and sequential circuits;
synchronous and asynchronous circuits;
example: asynchronous counter and synchronous version using a finite-state machine.
Basic hardware circuits:
multiplexer;
demultiplexer.
Verilog programming language:
combinatorial (assign) and sequential (always) Verilog modules;
basic modules implementing basic hardware circuits:
multiplexer (synchronous and asynchronous version);
synchronous counter with set to a preset value, and reset;
blocking and non–blocking assignments.
Problems:¶
development of a stopwatch from 0 to 99.99 s (1/100 s resolution), with 2–digits BCD coding and a 2 x 4–LED array display;
development of a synchronous counter based on a “master clock”.
Types of Circuits:¶
Combinatorial circuits: just a bunch of logic gates put in cascade. There is no way to control the flow of information but, at the same time, you are using all the speed available.
Sequential circuits: circuits where a memory element is present. Usually, it is some kind of flip flop and, therefore, a clock is needed.
Asynchronous circuits: circuits where all the parts are clocked by a single master clock. It assures that all the submodules are synchronized and avoids race condition problems.
Synchronous circuits: different parts of the circuit are clocked with different clocks. Easier to implement and allows for part of the circuit to work at a higher speed. Mitigation for race condition is a handshake protocol where each module has to signal the end of its computation.
D Type Flip Flops¶
It is the simplest type of flip flop. At each clock cycle, it can be set to store a \(1\) or a \(0\) and it will hold it up to a change. It is the basic component of memories.
Multiplexers¶
(De)Multiplexers are asynchronous combinatorial circuits that allow transmitting data from \(n\) different lines with a single data cable and \(ceil\left(log_2(n)\right)\) selector lines. Only one line can be active at a given time.
