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Nov 17, 2016 · The main difference between latches and flip-flops is that for latches, their outputs are constantly affected by their inputs as long as the enable signal is asserted. In other words, when they are enabled, their content changes immediately when their inputs change.
Aug 12, 2022 · The difference between a latch and a flip-flop is that a latch is asynchronous, and the outputs can change as soon as the inputs do (or at least after a small propagation delay). A flip-flop, on the other hand, is edge-triggered and only changes state when a control signal goes from high to low or low to high.
- Sequencing
- Sequencing Overhead
- Flip-Flop Designs
- Reset
- Set / Reset
- Contamination and Propagation Delays A
- Time Borrowing
- Clock Skew
- Clocking realities
- Metastability - MTBF
- MTBF: Alternate definition
- Preventing Metastability
- Simulating Metastability
- Slave internal
- Dynamic Latch Design (cont.)
Combinational logic (CL) output depends on current inputs Sequential logic output depends on current and previous inputs Requires separating previous, current, future Called state or tokens Ex: FSM, pipeline Sequencing (cont) If tokens moved through pipeline at constant speed, no sequencing elements would be necessary Ex: fiber-optic cable Light pu...
Use flip-flops to delay fast tokens so they move through exactly one stage each cycle Inevitably adds some delay to the slow tokens Makes circuit slower than just the logic delay Called sequencing overhead Some people call this clocking overhead But it applies to asynchronous circuits too Inevitable side effect of maintaining sequence Basic
§ Flip-flop is built as pair of back-to-back latches
Force output low when reset asserted Synchronous vs. asynchronous
Set forces output high when enabled Flip-flop with asynchronous set and reset
Combinational Logic clk D Q clk D Q Y A Y clk t setup thold D tpcq Q tccq clk D t pdq tcdq Q tccq tsetup tpcq thold
In a flop-based system: Data launches on one rising edge Must setup before next rising edge If it arrives late, system fails If it arrives early, time is wasted Flops have hard edges In a latch-based system Data can pass through latch while transparent Long cycle of logic can borrow time into next As long as each loop completes in one cycle Time Bo...
We have assumed zero clock skew Clocks really have uncertainty in arrival time Decreases maximum propagation delay Increases minimum contamination delay Decreases time borrowing Clock Skew: Flip-Flops
If setup times are violated, reduce clock speed Useful clock skew can be your friend Jitter is NEVER your friend Pulse latches do not scale well from generation to generation Use them if you want lot’s of debugging experience J Metastability is very real (and deadly) Lastly, if hold times are violated, chip fails at any speed and PVT You have a “br...
The C1 and C2 constants depend on the device process and operating conditions. Determined empirically. fCLK is the clock frequency of the clock domain receiving the asynchronous signal fDATA is the toggling frequency of the asynchronous input data signal. Faster clock frequencies and faster-toggling data reduce (or worsen) the MTBF. The tMET parame...
To avoid synchronizer failure wait long enough before using a synchronizer’s output. Where “long enough”, is the mean time between synchronizer failures and is several orders of magnitude longer than the designer’s expected length of employment! John Wakerly
§ The tMET for a synchronization chain is the sum of the output timing slacks for each register in the chain. Courtesy Altera
Tsu : : input setup time Thold : input hold time Tcq clock to out Tdata to out = Tsu + Tcq Simulating Metastability (cont.)
Dout Functional Pass/Failure vs. Tsu and Th High Speed Flip-Flop for Synchronization High Speed Flip-Flop for Synchronization (cont.)
Transmission gate No Vt drop Requires inverted clock f f Q Inverting buffer Restoring No back driving Fixes either Output noise sensitivity Or diffusion input Inverted output f D D f X Q f f Q
Table of Contents. What is a Flip-Flop? Difference Between Flip-Flops & Latches. Types of Digital Flip-Flops. SR Flip-Flop. D Flip-Flop. JK Flip-Flop. T Flip-Flop. Application of Digital Flip-Flops. What is a Flip-Flop? Digital flip-flops are memory devices used for storing binary data in sequential logic circuits.
A flip-flop samples the inputs only at a clock event (rising edge, etc.) A Latch samples the inputs continuously whenever it is enabled , that is, only when the enable signal is on. (or otherwise, it would be a wire, not a latch).
May 28, 2021 · It is said to trigger on the edge of the clock pulse, and thus is called an edge-triggered flip-flop. The flip-flop can be triggered by a raising edge (0->1, or positive edge trigger) or falling edge (1->0, or negative edge trigger).
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Oct 3, 2024 · The main difference between them is how they react to changes. A latch changes its output whenever its input changes. This means it’s always ready to respond. On the other hand, a flip-flop only changes its output at specific moments, like when its control signal goes from low to high.
