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For differential inputs, it is measured between the

crosspoints of the rise and fall transitions as shown in

Figure 31.

Figure 31. Differential Input Pulse Width

tPW

VIH

VIL

Xpt

Setup and Hold Time

Applicability – Only synchronous clocked devices have

setup (tS or tSETUP) and hold (tH or tHOLD) times.

Timing Window – The minimum setup requirement and

the minimum hold requirement specify the timing window

where the input must not change in order to successfully

clock the input. The setup time specifies the left edge of the

timing window, and the hold time specifies the right edge of

the window. Both timing requirements must be met in order

to successfully clock the input.

Measurement Points – Differential crosspoints (refer to

the “Differential Characteristics” section) and single−end

50% points (refer to the “Single−Ended Characteristics”

section) are used as time measurement points. Note from the

following figures that the 50% point of the active clock edge

is the time origin of all setup and hold time measurements.

Minimum Setup Time – The following is true of

minimum setup times.

• Minimum setup times are usually positive, and they

specify the minimum length of time that the input must

remain unchanged before the active clock edge in order

to successfully clock the input. Positive setup times

therefore indicate that the left edge of the timing window

is before the active clock edge.

• Negative minimum setup times specify the minimum

length of time that the input must remain unchanged

after the active clock edge in order to successfully clock

the input. Negative setup times therefore indicate that

the left edge of the timing window is after the active

clock edge.

Minimum Hold Time – The following is true of

minimum setup times.

• Minimum hold times are usually positive, and they

specify the minimum length of time that the input must

remain unchanged after the active clock edge in order

to successfully clock the input. Positive hold times

therefore indicate that the right edge of the timing

window is after the active clock edge.

• Negative hold times specify the minimum length of

time that the input must remain unchanged before the

active clock edge in order to successfully clock the

input. Negative hold times therefore indicate that the

right edge of the timing window is before the active

clock edge.

Typical Setup and Hold Times – The typical setup and

hold times specified on data sheets are not guaranteed, and

they are only included for failure analysis calculations. They

are measured by independently moving the left and right

edges of the timing window about the active clock edge until

the outputs no longer function properly.

Positive Setup and Positive Hold Example – The

MC100EP29 data sheet specifies the following:

• The minimum setup time of positive 100 ps indicates

that the left edge of the timing window is 100 ps before

the active rising clock edge.

• The minimum hold time of positive 100 ps specifies

that the right edge of the timing window is 100 ps after

the active rising clock edge.

The setup time requirement and the hold time requirement

were both met in the example shown in Figure 32, therefore

the LOW−to−HIGH output transition occurs after the CLK

rising edge propagation delay of 420 ps. Note that the input

cannot change within the timing window of 200 ps. Only

one side of the differential clocks, inputs, and outputs are

shown in Figure 32.

Figure 32. Positive Setup and Positive Hold Example

t(ps)

CLK

50%

INPUT

OUTPUT

tPHL

420 ps

+100

ts(min)

+100

th(min)

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