The most basic of all the bistable latches and bistable multivibrators is the set-rest (SR) flip-flop. So to help us understand better the different types of flip-flops available, the following sequential logic tutorial shows us how we can make the conversion of flip-flops from one type to another simply by modifying the inputs of a particular type of a flip-flop starting with the SR flip-flop. There are basically four different types of flip flops and these are: These two digital gates produce two stable outputs both HIGH and LOW in which one is the complement of the other.īut we can make many different types of flip-flop circuits both asynchronous and synchronous (an asynchronous flip-flop does not require a clock signal input, but a synchronous one does) from either basic cross-coupled NAND Gates and NOR Gates with the conversion of flip-flops between the different types sometimes a bit confusion. The basic bistable multivibrator is a type of regenerative circuit that has two active digital gates designed so that when one digital gate conducts, the other gate is cut-off and vice versa. By using cross-coupled gates and feeding the output from one gate to the input of the other, (inputs-outputs interchanged) the circuit has a closed-loop (positive feedback) so its output depends on the state of the inputs, making the circuit sequential and having memory.įlip-flops also belong to a category of digital switching circuits called Multivibrators. The most basic way to create a single one-bit flip-flop is to use two NOR gates gates as shown.

Also, memory elements made from bistable latches form the basis of accumulators and registers on which a computer, or micro-controller, does its complex arithmetic. The interconnection of digital logic gates to produce a memory device leads to applications such as switch debounce circuits, shift registers and counters, etc. However, sequential logic circuits do have memory and therefore use various types of flip-flop designs to remember their present states. Note that a combinational logic circuit does not require any form of memory and therefore does not use flip-flops. We have also seen that the bistable flip-flop is the most basic storage element in a sequential logic circuit and can be configured to produce simple memory elements by interconnecting two inverting gates to generate feedback. We have seen throughout this Electronics Tutorial section on Sequential Logic that a flip-flop will remain in one of its two stable states indefinitely until some form of external trigger pulse is applied to make it change state.Īs flip-flops are bistable devices, these sequential circuits are sometimes called “latches” because their outputs are locked or latched onto their input state until there is another change to its input condition.

Side note: yes, at one point in history computers were built out of relays.The conversion of flip-flops from one type to another is not as complicated as you may think.

It's something you could reasonably test in the lab and it's pretty close to what you will likely see in practice. Putting combinational circuits together with sequential circuits makes finite state machines, which lead to more complex machines like computers.Ībstract ideas are powerful but can be hard to grasp without a specific example, that's why your coursework is focusing on SR latch as a specific example of a simple sequential circuit element. You're not studying a technology, you're studying the underlying design principles.Īrithmetic operations (such as unsigned 2's complement addition and subtraction) can be made from Combinational circuits (gates).

Same basic design principles apply to all sequential circuits, regardless of the underlying technology. Could also be built from vacuum tubes or op-amps (with positive feedback and hysteresis) or some types of mechanical relays or even mechanical cogs and gears.

A Set-Reset latch made of cross-coupled NOR is just one example of a way to realize a sequential circuit. 'Sequential circuits' is an abstract idea.

Sequential logic circuit