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# How to calculate Ts,Th,Tclk,Tpd

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#### phutanesv

##### Full Member level 2
tpd using tcd

Dear dude,

Consider a block and they are arranged as

In------->combo1------> R1-------->combo2---------> R2--------> Out

How to calculate Ts,Th,Tclk,Tpd

combo block CL1 which has Tpd=3,Tcd=1

Register R1 Tpd=2,Tcd=1,Ts=3, Th=2

Combo block CL2 Tpd=5,Tcd=1

Register R2 Tpd=8, Tcd=2,Ts=4

Phutane

You cannot calculate Ts and Th . they are const. for a flip flop..

Dear dude ubna,

For the block, th hold time is calculated as 2
Ts=6
tcd=2
tpd=8
tclk=11

How did this get

phutane

Tclk >= Tpd(reg1)+ Tpd(comb logic2) + Ts(reg2) = 2+5+4 =11

Tsu = Tpd(comb1) + Ts(reg1) = 3+3 = 6
Th = Tcd(comb1) + Th(reg1) = 1+1 = 2

Added after 3 minutes:

Tpd is same as Tpd of reg2

Dear Mega star,

You have given the answer ,fine,

But i need little clarification

In case of Tclk>=Tpd reg1+Tpd (combo2)+Ts (reg2)=2+5+4=11

In this case the Clk has to propagate from R1 so Tpd (reg1)

then it has propagate thro Combo2 So Tpd (combo2)

Then Setup time of Reg2 so Ts (reg2)

My question is y did u consider Ts of Reg1, it is similar to Reg2 side since clk is propagating into Reg2 too,

2) In Th calculation you have considered as Tcd combo1+Th reg1=1+2=3

I did not understand, pls help me

Added after 16 minutes:

Dear Mega star,

You have given the answer ,fine,

But i need little clarification

In case of Tclk>=Tpd reg1+Tpd (combo2)+Ts (reg2)=2+5+4=11

In this case the Clk has to propagate from R1 so Tpd (reg1)

then it has propagate thro Combo2 So Tpd (combo2)

Then Setup time of Reg2 so Ts (reg2)

My question is y did u consider Ts of Reg1, it is similar to Reg2 side since clk is propagating into Reg2 too,

2) In Th calculation you have considered as Tcd combo1+Th reg1=1+2=3

I did not understand, pls help me

For first question, i didnt consider Ts of REg1 bcos the data path starts from clk->q of Reg1(for FF,start point is clk pin and end point is D pin). In anotherway,Setup time is always checked at Capture FF but not with Launch FF. For example, path In-->comb1-->reg1 ,u shud consider Ts of reg1 bcos reg1 is caputring FF. You should calc requred time in 3 paths(ie. input to reg1,reg1 to reg2 and re2 to output).The max valus is taken clock period.

Regarding second question, the tcd of comb1 + tcd of Reg1 >= Thold of Reg1. with this equation, 1+1 >= Thod of FF1.

I hope you got it now.

### phutanesv

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