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Difference between a flip flop and a Scan flip flop

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vlsi_fanatic

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Can any one explain me the difference between a flip flop and a Scan flip flop?

thanks
 

yuzhicai

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scan flop

A scan flip flop has a scan logic base on a flip flop , generally it is a mux for d and clk.
 

smith_kang

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scan flops

hi
Scan FF contains a MUX to select either a Normal opration with Data input or Scan opration with Scan Input.It has a control input to select either data or scan input.It is bigger tahn Normal FF(as MUX included here).It adds nearly 20-30% of area per FF.

hope it will clear your doubt.
 

akrlot

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scan d flip flop

see here the difference:
**broken link removed**

hope it helps.
BR
 

viswa

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scan dff

a scan flip flop is ordinary flip flop modified for sake of using it during dft.it has additional scan input and scan output for sending test inputs and receiving test outputs.in addition it has scan clock for clocked scan flip flops or scan enable for muxed flip flops.

hope ur doubt would have been cleared.
 

cedance

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scan flip flop

hi,

they are very similar to the flipflops with an additional enable pin enabling them to function both as an ordinary flip flop as well as the scan flipflop. they are very much conceptuially related to "design for tesability"... or more promptly for fault simulation purposes. inorder to check th current state of the flip flop ensuring the rightness of the state. the enable pin decides the action of the flip flop.. as to whetrher its operating mode or the testign mode.

if in the testing mode.. then the path to be selected is first identified and then the test vectors for the corresponding stages are assigned accordingly and hte o/ps arrived are verified for the checking of the functionality of the flip flops.

u could refer to any "design for testability" books found in this forum to get to know more abt this!

am not sure if these books ll have the content exactly u would require.. but would help u understand better.. i think.. atleast one of these..






hope this helps! :0


/cedance
 

FLEXcertifydll

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wiki scan flop

A Flip-flop in scan chain which is scanable flip-flop. There is D and scan_in MUX link to flip-flop input.
 

ken_ooi

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scan flip flops

Normal Flip-Flop have D, Clk & Q.
Scan flop have D, SI (scan in), SE (scan enable), Clk, Q and/or SO (scan out).
During scan shift operation (SE=1), data will shift in through the SI pin.
Durig scan capture state (SE=0), data will capture into the scan flop via D pin.
 

arunragavan

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lssd flop

these are basic d flip flops which are used as an alternative for ordinary flip flops.. they are used during testing and much prefered over BIST units.

scan flops have D, Q and clk.. like SI (Scan Input) == SO (scan output)


with regards,
 

crazy_man

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flip flop scan

Sacn flops are basically flops used to perform DFT...
 

power-twq

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scan flipflops

a scan dff has three extra pins than a normal dff,

scan_en, si, so.


vlsi_fanatic said:
Can any one explain me the difference between a flip flop and a Scan flip flop?

thanks
 

waranp

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lssd type scan cell for edge triggered flop

In generally, what is the area difference between a dff and a scan dff? Thanks a lot!
 

dr_dft

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scanning flip flop

waranp,

The size difference really depends on what type of non-scan and scan flip-flop you are talking about.
In general, the mux-D scan flip-flop has the smallest area increase (a single mux), but if you have a dedicated scan output, then there is some bufferring involved.
The next area-efficient flip-flop is the clocked scan, where you usually have a separate scan clock which is edge triggered. This can usually be done with an additinal latch stage.
The more expensive flip-flop is the LSSD type, where there are normally one or two extra latches, and two scan clocks, but it is the safest because you eliminate any hold time isses with the two non-overlapping scan clocks.
So in general, the difference can be anywhere from just a few percent area increase to almost double the size of the flip-flop. Usually you can tell by looking at the datasheet of your standard cell library.
 

arbalez

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scanable flip flop

can someone here include the behavioral code of scan flops? i need to know how it works.
 

dr_dft

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flip flop inputs si se

module sdff ( d, si, se, ck, q );
input d; // functional input
input si; // scan input
input se; // scan enable
input ck; // clock
output q; // data output

always @(posedge ck)
q <= se? si : d;

endmodule
 

linli

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what is scan flip flop

normally it has a pin called SI to let you connect the scan-chain
 

anjali

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scanflop

dr_dft said:
waranp,

The more expensive flip-flop is the LSSD type, where there are normally one or two extra latches, and two scan clocks, but it is the safest because you eliminate any hold time isses with the two non-overlapping scan clocks.


why it is safest? please explain.

i feel latches are not handled easily in backend. is it correct?

Added after 35 minutes:

dr_dft said:
waranp,

The more expensive flip-flop is the LSSD type, where there are normally one or two extra latches, and two scan clocks, but it is the safest because you eliminate any hold time isses with the two non-overlapping scan clocks.


why it is safest? please explain.

i feel latches are not handled easily in backend. is it correct?
 

dr_dft

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mux scan d flip flop

LSSD is safest in terms of no hold time checks are required for the shifting part of the scan flip-flops, since the 2 shift clocks can always be tuned on the ATE to remove any hold time issues. Even though the scan portion of the flip-flop is LSSD type, the functional data input can still be an edge triggered flip-flop, which can be handled by a normal ASIC flow.
Not many ASIC libraries use LSSD. The most well known ASIC vendor who uses it is IBM.
 

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