Sequential Circuits #

In combinational circuits, the outputs are only dependent on the inputs. In sequential circuits, the outputs depend on the inputs, and the previous state of the circuit.

Core modules #

S-R Latches

• Latches are basic building blocks of flip-flops (basic memory unit)
• A 1 bit latch will store 1 bit, 4 bit latch stores 4 bits, and so forth …
• Two types of memory elements based on the type of trigger that is suitable to operate
• Latches, asynchronous
• Latches operate with an enable signal, which is level sensitive

D flip-flop

• Basic memory storage device
• Block diagram of a D flip flop
• Flip flops, synchronous (the device samples its input based on a common clock)
• Flip flops are edge sensitive
• Doesn’t sample an input unless a clock comes in, clock signal needed to change states
• D flip flops is designed using S-R latches
• Similar to S-R latch, only we use set and reset function. (Ties D input to S and NOT D to R).

S-R flip flop with NOR gates #

Finished in next lecture