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edge vs level triggering

Hi,

Appreciate if anyone could explain me the significance of edge
triggering vs level triggering. I know what they are but don't
understand the significance except in interrupts. Where do we need
edge triggering and where do we need level triggering. Is this
applicable only for clock signals? or for data inputs as well? why?

Thanks in advance
mr
 
R

Ross Herbert

Jan 1, 1970
0
Hi,

Appreciate if anyone could explain me the significance of edge
triggering vs level triggering. I know what they are but don't
understand the significance except in interrupts. Where do we need
edge triggering and where do we need level triggering. Is this
applicable only for clock signals? or for data inputs as well? why?

Thanks in advance
mr


In simple terms, a voltage level may not be well defined for
repeatable and reliable triggering, whereas an edge is an edge and is
always well defined regardless of level. As long as the edge has a
fast rise or fall time, we can select which edge we want to trigger on
and always achieve repeatable results.
 
J

John Barrett

Jan 1, 1970
0
Hi,

Appreciate if anyone could explain me the significance of edge
triggering vs level triggering. I know what they are but don't
understand the significance except in interrupts. Where do we need
edge triggering and where do we need level triggering. Is this
applicable only for clock signals? or for data inputs as well? why?

Thanks in advance
mr

an edge triggered latch is probably the perfect example -- you only want to
latch the data bit on the edge of the strobe, and ignore changes while the
strobe is at high level, potentially because the input to the latch is
effected by the output of the latch, and if the latch were level triggered,
it would continue to accept changes in the input data -- think edge
triggered as "leading edge triggered" and of level triggered as "trailing
edge triggered" !!!

another interesting example is the master/slave flip-flop -- data is latched
into the master on the rising edge (output from the slave remains stable,
further changes in the inputs ignored), and transfers the data to the slave
and the outputs on the falling edge... just another way to make sure the
data changes exactly when you want it to.
 
T

Tam/WB2TT

Jan 1, 1970
0
Hi,

Appreciate if anyone could explain me the significance of edge
triggering vs level triggering. I know what they are but don't
understand the significance except in interrupts. Where do we need
edge triggering and where do we need level triggering. Is this
applicable only for clock signals? or for data inputs as well? why?

Thanks in advance
mr
The simplest case I can think of is to compare a 74x74 edge triggered Dff to
a 74x573 transparent latch. The '74 output will go to the state the input
was in just before the clock edge. The '573 output will follow the input the
whole time that the enable is active.

Somebody mentioned master slave FFs. You can make one out of a pair of '573s
running on opposite clock phases. But, when the level changes, that is
really an edge as far as setup and hold times go.

TYam
 
K

krw

Jan 1, 1970
0
an edge triggered latch is probably the perfect example -- you only want to
latch the data bit on the edge of the strobe, and ignore changes while the
strobe is at high level, potentially because the input to the latch is
effected by the output of the latch, and if the latch were level triggered,
it would continue to accept changes in the input data -- think edge
triggered as "leading edge triggered" and of level triggered as "trailing
edge triggered" !!!

No, a "level triggered latch" is not "trailing edge triggered" (nor
"triggered" at all). An edge-triggered flipflop will only change
state on the specified edge of the strobe/clock and hold state at
all other times. A level sensitive latch will change state
whenever the enable is active and hold state when the enable is
inactive.
another interesting example is the master/slave flip-flop -- data is latched
into the master on the rising edge (output from the slave remains stable,
further changes in the inputs ignored), and transfers the data to the slave
and the outputs on the falling edge... just another way to make sure the
data changes exactly when you want it to.

Take two level sensitive latches and put an inverted between the
enables (with appropriate care for timing ;) and you get an edge
triggered master-slave flipflop.
 
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