FIFO Vs Shift Register


Q1.What does FIFO depth mean. Q2.How can i use FIFO to register the signals comming out of FPGA. Q3.How would i address the FIFO. Q4.Can i use Shift register to save incomming outside signals. Q5.How can i address Shift registers. Q6.What is the difference b/w FIFO and shift register

I am trying to design a I/O logic how can i use FIFOs or shift registers in it



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C'mon, Faraz. At least make a little effort to research this on your own. Ever heard of Google?


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FIFOs are used mostly to store data streams and the depth is the number of storage locations available. The Width, on the other hand, is the number of bits in one data, usually 1, 8, 16, 32, or 64 bits.

You apply the signals to the FIFO input, tell the FIFO when to store data with a write enable signal, and read the data off the output with a read enable.

FIFOs are different than Memory in that they do not generally have an address. You put data into a FIFO and pull it off later in sequence.


Shift registers are a little different in that each output can be brought out as a separate output. These are sometimes called taps. Large FIFOs are usually built using a memory and two counters that supply the write address and the read address.

Mostly its the taps. Also, there is usually a significant clock delay in a shift register depending directly on its depth because data is shifted from one resgister to the next in a chain. There are special case shift registers called fall-through that is an exception to this. A FIFO built with read and write counter addresses, the delay can be as little as one clock cycle.

One area that FIFOs are used is to straddle data between two circuits running on different clocks. These are called asynchrounous FIFOs.

Brad Smallridge Ai Vision

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Brad Smallridge

How many meters under water it's operating. ( Feet in US )

Be sure it signs in before giving it the key to the memory pool.

Hello FIFO!

Only if they really want to be saved. Prayer helps.

Howdy! (Shift registers are far less formal)

About 2 pounds. ( 1 Kg outside US )

No Homework!

Review the excellent app notes to be found on vendors web sites. For Xilinx, you might start with xapp465, then go on to xapp256...they have a very good pile of useful information. You might end up learning more than just the answers to your questions.

(sorry folks, it's been a 65+ hour work week)

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