D flip-flop with synchronous reset in Verilog - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a D flip-flop with synchronous reset?

A D flip-flop with synchronous reset is a memory element that stores the input value (D) on the rising edge of the clock, but if the reset signal is active during the clock edge, it sets the output to zero instead of the input value.

beginner

In Verilog, how do you describe a synchronous reset inside an always block?

You check the reset signal inside the clock edge condition, usually with an if statement before assigning the D input to the output. For example: if (reset) q <= 0; else q <= d;

beginner

Why is the reset called synchronous in a D flip-flop with synchronous reset?

Because the reset only affects the output at the clock edge, meaning the reset signal is synchronized with the clock and does not change the output asynchronously.

beginner

Write the sensitivity list for a D flip-flop with synchronous reset in Verilog.

The sensitivity list includes only the clock signal, for example: always @(posedge clk) begin ... end

beginner

What happens if the reset signal is low during the clock edge in a D flip-flop with synchronous reset?

The flip-flop stores the value of the D input into the output Q at the clock edge.

In a D flip-flop with synchronous reset, when does the reset affect the output?

A Immediately when reset is activated

B Only at the clock edge

C Only when the clock is low

D At any time asynchronously

The reset is synchronous, so it only affects the output at the clock edge.

Which signal is included in the sensitivity list of a synchronous reset D flip-flop in Verilog?

A clk only

B reset only

C clk and reset

D d and reset

Only the clock signal is in the sensitivity list because reset is synchronous and checked inside the clock edge.

What is the output Q when reset is active during the clock edge in a synchronous reset D flip-flop?

A Undefined

B 1

C Same as D input

D 0

When reset is active, output Q is set to 0 synchronously at the clock edge.

How do you write the reset condition inside the always block for synchronous reset?

A if (reset) q = 0; else q = d;

B if (reset) q <= d; else q <= 0;

C if (reset) q <= 0; else q <= d;

D if (reset) q = d; else q = 0;

The reset sets output to 0; otherwise, output follows input D.

What type of flip-flop behavior does a synchronous reset NOT have?

A Immediate reset without clock

B Reset at clock edge

C Data storage on clock edge

D Reset checked inside always block

Synchronous reset does not reset output immediately; it waits for the clock edge.

Explain how a D flip-flop with synchronous reset works and how it differs from an asynchronous reset flip-flop.

Think about when the reset changes the output.

Write a simple Verilog code snippet for a D flip-flop with synchronous reset and explain each part.

Focus on the clock and reset handling inside the always block.