74F525SCX datasheet(3/10 Pages) NSC

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Functional Description (Continued)

Function Table

Function

Mode 0

Mode 1

Mode 2

Mode 3

Mode 4

Mode 5

Mode 6

Mode 7

MODE 4 Interval Timer Pulse Output with Count Hold

While XTR is HIGH the data in the data latches is loaded

into the counter upon the next positive edge of CP The

negative edge of XTR enables the count-down to begin with

the next positive edge of CP When the count reaches zero

Q normally low is brought HIGH for a single period of CP

Q2 toggles state on the positive edge of Q Taking XTR

HIGH before the counters reach zero stops the count-down

from the point where it was held Data cannot be reloaded

into the counter until a count of zero is reached See

Figure

MODE 5 Interval Timer Inverted Pulse Output with

Count Hold

The operation is exactly the same as Mode 4 except that Q

is normally HIGH and goes LOW for a single period of CP

Q2 toggles on the negative-edge of Q See

Figure 3

MODE 6 Retriggerable Synchronous One-Shot

When XTR is HIGH the data in the data latches is loaded

into the counter upon the positive edge of CP The negative

edge of XTR enables the count-down to begin with the next

positive edge of CP wehre Q normally LOW is then

brought HIGH and the counter is decremented when the

count reaches zero Q is brought LOW and Q2 is toggled

Bringing XTR HIGH during the count-down will allow the

data in the data latches to be loaded into the counter with

the next positive edge of CP but will not affect Q See

Fig-

ure 4 NOTE that the pulse width of Q will be N-1 clock

cycles where N is the number loaded into the counter

Ne1 should not be used as this may cause unpredictable

results

MODE 7 Frequency Generator

When XTR is HIGH the data in the data latches is loaded

into the counter upon the positive edge of CP The negative

edge of XTR enables the count-down to begin with the next

positive edge of CP When the count reaches zero Q nor-

mally LOW is brought HIGH for a single period of CP and

Q2 is toggled The same clock edge that brings Q HIGH

also loads the data in the data latches into the counter The

counter will start to count on the next positive edge of CP

This mode will run continuously after an initial XTR until

stopped by MR Taking XTR HIGH at any time causes the

data in the data latches to be loaded into the counter and Q

output to be cleared with the next positive edge of CP See

Figure 5

Block Diagram

TLF9547 – 4

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