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When stimulus
data is forced out
to your DUT input pins it may need to be applied in a certain way. We
already
know, for example, that very often the data must be present at input
pins before
the clock edge occurs, allowing sufficient setup time. Stimulus formats
help us
to shape the stimulus data to conform it to follow the needs of your
chip. You
can select the stimulus for your inputs only in the Pin Setup window.
Here's a
description of the different types of stimulus formats:
NRZ stands for
"Non Return to Zero".
With this
format, you can place the delay time for the
start of the assertion anywhere in the cycle. Vector data is forced for
each
vector at a point in time specified by this delay value.
It remains asserted for a period equal to
one entire test rate clock period. If you specify Leading edge delay to
be
10ns, then the stimulus seen at each vector will be "forced" after a
10ns delay from the start of each vector and will continue for 10ns
into the
next vector. This mode is often used for address pins and non-I/O data
pins.
Testing your part with all pins defined as NRZ is known as
"settled-state" testing, because data is held present on the pins for
a much longer period than sometimes necessary to allow everything to
"settle" before changing data.
RZ means
"Return to Zero".
If a "1"
appears in the
vector, it is asserted after the leading edge delay time and then the
tester
driver returns back to zero after the trailing edge time. The duration
of the
force is:
TT - TL
meaning
"trailing time minus leading time". If a zero appears then the output
is unchanged for that vector. This format is commonly used for clocks,
enables,
strobes, and anywhere that control over both edges of stimulus is
needed
(dynamic data).
R1 means
"Return to One".
This dynamic
mode of operation performs in much the
same way as Return to Zero, except that the active data state is
reversed. If a
Master Reset pin is active low
you can use R1 to hold the pin in the
logic high state (i.e., "ones" in the vector data) until a reset is
desired, and then apply a logic low (zero in the vector data) for a
given
period. See the example to compare differences between formats.
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R Inhis "Return to Inhibit".
As you can see in the
drawing,
this mode is a bit similar to R1 or RZ, except that the "Return to"
point allows both R1 and RZ to affect change. You must set valid values for Leading and Trailing edges
to control duration
of the "pulse".
RC: Return
to
Compliment.
More accurately, Surround
by Compliment. We have retained
"RC" as the name because it complies well with the understanding of
this format.
Special Note on SCIO
When you
select Split Cycle I/O as your data direction
and use NRZ as the Stimulus format, your expected data should always be
the
same as your stimulus data, or else masked when the tester is driving.
When
your data is in the "Output" mode the tester is not driving, and can
capture the output of your DUT. But when the tester is driving, it is
unlikely
that your DUTs outputs will overcome the tester drivers thereby making
a
compare only of the drivers state. When
using any of the "Dynamic" formats, place your compare strobe away
from the "pulse" created by your stimulus data. View your vectors in
the Graph window to check your timing.
Related info
Q'nApp #S1: The PinList function
Qs17.zip is a zipped Word file
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