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# Combinational Logic Design

89 Threads found on edaboard.com: Combinational Logic Design

## FPGA , where it programs the sequential logic and cobinational logic of a Design.

b. Configuration logic Block (CLB) which contains the LUT to perform combinational logic.

## [verilog] How is a always@* block synthesized

A always @* block will never produce a flip-flop in a design it might produce a latch if there is feedback, otherwise you get a combinational blob. The reg keyword does not by definition produce flip-flops it only means the signal will hold state until changed by an assignment. This is part of the reason for changing it to logic in SV. (...)

## Average Power consumed by combinational logic in IC : after pnr ; ptpx

Hi, Typical power consumed by a clock tree in the design is around 40-45% What is the typical or on an average power consumed by combinational logic cells in the design after pnr. Thanks

## Methods to fix timing violations in synthesis stage

I can only answer it at a very top- (concept-) level. In order to reduce the negative slack, try to reduce the combinational logic between two the two registers (flip-flops). Or adding a pipeline can also be a solution. If your design is big, try out 'incremental compilation' to achieve timing closure for a particular partition that (...)

## FinFET circuit design for DPA

I am not using a clock. I have a universal logic cell which I'll use in the design of combinational and sequential circuits.

## Can Scan shift frequency be faster than capture frequency?

it's really dependent of your design, I means, a design with huge combinational logic, could have a lowest speed than the pad shift in/out, the pad sees very "high" capacitance which limit the shift speed.

This circuit definitely has to be clocked. Else the tool reports it as a combi loop. You can have a 2:1 mux before giving the 3rd input to the adder. The flop must be in the path from the output to back to Cin while the adder should be combinational logic.

## Loop exceeded maximum iteration limit. (ELAB-900) and increase the limit

Hi, I got the Loop exceeded maximum iteration limit. (ELAB-900) error in synopsys design vision. I am aware that it is not a proper usage of for in verilog. I am trying to generate a large combinational logic, that's way I need to use for loop in always@(*) statement. I was wondering if there is a way to increase the ma

## how can i find false path in design by design compiler?

well you did not find false path. your synthesis has some timing issue, so two possibilities: 1- the designer claims this path is false, so you could add this path to false in your SDC. 2- the designer claims this path is true, then you have a timing issue, to solve by pipeline or rewrite RTL to push combinational logic (...)

## Area optimization for a custom library using Synopsys Design Vision

Hi, I write a custom library for synopsys design vision which only consists of XOR, NOR, and IV (inverter or NOT). My plan is to synthesize a combinational logic such that the resulting netlist has minimum number of NOR gates. I write the library as flows: library(and_or_xor) { cell(NOR) { area : 1000; pin(A

## Help with VHDL code for multiplier

No issue after I added a fa.vhd file to the design. You do know this is a very large combinational circuit. Using Vivado it ends up with >60 levels of logic (LUTs) from a_in to y. Of course I didn't add any constraints to try and improve the timing. e.g. 105366 Regards

## How to reduce combinational node in FPGA design?

Hi all, I am using a low cost FPGA (EP2C5T144C6) and trying to compile my verilog code in Quartus II. The error message come out: Error (170011): design contains 5204 blocks of type combinational node. However, device contains only 4608. I have try to reduce some If,Else case but it has no big different. Is there any suggestions that i

## Verilog combinational logic implementation, assign or always?

Hello guys, Today I had a discussion about Verilog coding style with a senior engineer I personal prefer write combinational logic using assign For example, assign cnt_w = incr ? cnt_r + 1 : cnt_r; However, he said combinational logic should be coded using always for the following reason 1. Continuous assignment (...)

## how to calculate dynamic ir drop..

Roughly, in general, 1um net witdh could support 1mA. The question is how much high the pic of current is? Generaly if you have a clock design, after the rising edge all flops will consumme during the "skew" delay, and the combinational logic will change function of the new value in the flops. 1-Empiric way, you know the worst (...)

## set internal wire as clock in rtl compiler

Can I set internal wire in my design as clock signal. Command define_clock has option {pin | port} But I need to use as clock internal wire from combinational logic.

## design camparator 4 bit

hi can some one explain to me how design combinational logic with ic7483 output(c4,s4,s3,s2,s1) fpr comparator

## fitter report: Design utilises zero registers .

My compilation is succesfull but the fitter report shows zero registers utilised. This is an absurd. This is just a fact. Your design doesn't define any registers. I'm not sure if you know what a register is? It's a DFF in constrast to combinational logic. You'll need a clock edge sensitive always block to infer registers, or equiv

## [Power] Relation between power and clock on time in ASIC digital design.

The power consumption is when data changed, and the data change at clock edges, and due to the transition/clock tree skew, around the clock edges all flops could changed. And after that the combinational logic will be impacted as well.

## can we include any combi gates in scan chain?

The goal of the scan chain, is to shift in/out flops containts, so adding combinational logic during the shift phase will not help to check the functionality of the design, and I don't imagine the ATPG tool could understood the data generated by this logic. The maulin sleth's question need to be respond by govindareddy1233.

## clockgating methodology

1- for our experience more than 10years, we design low power chip, the manual gated clock instertion is well know control than what it is done by the tool, or we do not see interesting power reduction based on our gated clock design. 2- yes, a combinational logic is added on the clock network, but the clock tree tool handle (...)

## the output is shifted by one clock VHDL

The input is transferred to ouput on the rising edge of clk. It is not shifted. The problem is either in the testbench or a lack of understanding synchronous logic. Depending on the design purpose, you might want to code a pure combinational process without a clock.

## Unconstrained PAth in a fulladder design - DC

I have not seen adders described like this before. Why don't you do register the inputs A and B always @(posedge clk) begin A_reg <= A; B_reg <= B; end then do addition as combinational logic assign {cout,sum} = A_reg + B_reg + cin; then register the sum output always @(posedge clk) begin sum_reg <= s

## slack paths, reduce it in design

I believed you mean how to reduce the negative slack, I means reduce the combinational logic between two memories element (flip flop). Added pipeline is a solution.

## FSM encoding what is advantage of hot-one ?

Hi, I thought before that the hot-one encoding for FSM was used to decrease the critical path of the combinational logic and hence increase the design speed but I tried a FSM once with binary encoding and once with hot-one encoding and the hot-one encoding was worse in terms of both speed and area . Can somebody explain to me please ? Thanks

## [Design Compiler] Add combo logic in netlist

Hello all, How I can add fix combinational logic at the output of every FF's using design Compiler? How it is possible through tcl script? Thanks in Advance.

## difference between RTL and Gate-level timing for combinational logic and wires

Hi guys, sorry for may be asking a simple question. We know that for "Registers" in a design, the timing difference between RTL and Gate-level (timing) simulation cannot exceed the clock period minus the setup time because else there would be a setup time violation. Now can we say the same thing about combinational logic wires? or (...)

## Determining timing of the critical path of combinational logic in Quartus?

In Quartus, how can I determine the timing of the critical path of combinational logic, when I am still in the module design phase? I get no Fmax report, I think because in this particular module I have no feedback from state registers to the combinational logic. inputs=>combinational (...)

## AND-OR-INVERT gate significane

i read about AND-OR-INVERT gate in wikipedia that, by using this we can implement any type of logic with small number gates, but i want to know to how to design the combinational circuits using AND-OR-INVERT gate. Can you send me any links or pdf file for designing combinational circuits using AND-OR-INVERT (...)

## design of combinational circuits in vhdl

when using sequential code to design combinational logic in vhdl if completle truth table is not defined ,the synthesis tool implement______________which is not requried 1.clock buffer 2.buffer 3.flip flop 4.latch

## Asynchronous CPLD design

Of course. You can implement combinational logic, latches and FFs clocked from the data inputs.

## Can we use functions in design ? if yes what will be the synthesized

Each functional call will be synthesized as a separate combinational logic block.

## group ungroup - Design Compiler

I think you are right. You have to ungroup and then group again. Can you share your code to show the flip flops and combinational logic that you want to group? But why not do this grouping in RTL by putting the flip flops in a separate new module.

## combinational logic before synchronizer

hi every one... presently i am working on Questa CDC analyzer.. while running the tool, i am getting some violations violation (1). combinational logic before synchronizer. before synchronizer i am using one 2 input "OR" gate. both inputs are coming from clk1 domain. my synchronizer is working in clk2 domain. Now what is the solution for th

## For a complex clock generator subblock, how to handle CTS?

Hi Guys, I got a design(without PLL), which includes a "clock generator" driving the whole chip. The "clock generator" has one clock root and generate many clocks by using different logic circuits, especially there is no divider circuit! In other words, only logic gates in this subblock, but the combinational circuits (...)

## virtual clock definition

If you are defining virtual clock to constrain the combinational path of the design, it does not matter what frequency you assign to virtual clock. But it does matter that how much time do you allow for the combinational logic may be as a percentage of this clock period. And then it would matter. Now if this block which you (...)

## Combinational Logic Design for PLC

What are some ways to be organized when writing combinational logic? When I write combinational logic, I just do it as I go along and it often leads to confusion because combinational logic doesn't have any structure. I'm a lot more organized when writing sequential (...)

## What is the need of FSM?

gmish27, A Finite State Machine is just an abstraction to ease sequential/combinational logic design and synthesis. Of course you are not obligated to work out sequential/combinational logic by state-machines approach, but it is usually easier and clearer. Regards, Regnum

## Any good resource - understanding pipeline

In hardware the function of pipeline is implemented by inserting registers in the combinational logic. Long combinational path tends to cause low maximum frequency. If there is critical path in your design, you can use the pipeline to insert registers in the long combinational path to shorten it. Then the (...)

## Design a simple circuit based on combinational logic to double the output frequency.

design a simple circuit based on combinational logic to double the output frequency.

## generated clock at two different nodes but referring to same clock

No difference. but I'd be more comfortable to generate a clock on the flop output since setting a clock on combinational logic requires to use dont_touch so that it won't be optimized away.

## Timing Related problem

Ok, let me try. This is the original design: DFF DFF1 (.clk(CLK), .d(D1), .q(Q1)); DFF DFF2 (.clk(CLK), .d(D2), .q(Q2)); D2 = f(Q1); // f is the combinational logic, and has delay of 10ns, for example; After skew of clocks, the new design is: CLK_skew = BUF (CLK); DFF DFF1 (.clk(CLK), .d(D1), .q(Q1)); DFF DFF2 (...)

## Genetic Algorithm for combinational logic design

Hi I have a problem to implement Genetic Algorithm for designing combinational logic circuits. With inputing a truth table of two or more variables, the code must give the combination of gates which produces this output. I want to implement it on Matlab. Can anyone help me with the code or with how I can do it?

## Help me design a combinational circuit

Hi All, design a combinational circuit that gives a active high signal whenever the input is perfect square..and also please provide vhdl logic also Thanks Rahul

## combinational circuit design:RTL to GDSII

Dear all, How can i give constraints to a combinational design in SDC format. wt all the RC commands and basic constraints for a combination design? kindly help Thankx in advance

## Digital clock design help required

I want to make a digital clock using combinational logic gates flip flops counters registers and full adders. Can any one please help me. If any online resources please provide me the links. Regards,

## Digital clock design help required

I want to make a digital clock using combinational logic gates flip flops counters registers and full adders. Can any one please help me. If any online resources please provide me the links. Regards,

## converting HEX coming from pic16f877 to ASCII

Can''t you change the code in the PIC to output ASCII itself? That will be the simplest and the most sensible solution. Otherwise you can just design a simple combinational logic to convert Hex to ASCII.

## interview qstn on comb ckt to remove less time pulse

hello all,i faced an interview yesterday and was stuck with one particular question of digital design. the question is as design a combinational logic which takes a train of pulses with different pulse width (1ns - 5ns) and produces pulses of only 5ns as should discard pulse widths less than 5ns. help appreciated. i (...)

## 2's complement in verilog

Hello, Your main problem is that you are trying to use initial blocks to model combinational logic. Initial blocks are not synthesizable and therefore should not be used to design any actual circuits. You should try moving this into an always block. The simple way to take a twos complement in verilog is to invert and add 1. For instance: (...)

## interview question.combinational circuit frequency division

1)design a simple circuit based on combinational logic to double the output frequency 2)design a combinational circuit that can divide the clock frequency by 2. thanks