MC14541B

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5

TYPICAL RC OSCILLATOR CHARACTERISTICS

Figure 4. RC Oscillator Stability

Figure 5. RC Oscillator Frequency as a

8.0

4.0

0

– 4.0

– 8.0

–12

–16

125

100

75

50

25

0

–25

–55

10 V

5.0 V

C = 1000 pF

100

0.1

0.2

0.5

1.0

2.0

5.0

10

20

50

1.0 k

10 k

100 k

1.0 m

0.0001

0.001

0.01

0.1

C, CAPACITANCE (

µF)

f AS A FUNCTION

(C = 1000 pF)

f AS A FUNCTION

OF C

OPERATING CHARACTERISTICS

With Auto Reset pin set to a “0” the counter circuit is

initialized by turning on power. Or with power already on,

the counter circuit is reset when the Master Reset pin is set

to a “1”. Both types of reset will result in synchronously

resetting all counter stages independent of counter state.

Auto Reset pin when set to a “1” provides a low power

operation.

The RC oscillator as shown in Figure 3 will oscillate with

a frequency determined by the external RC network i.e.,

if (1 kHz

v f v 100 kHz)

1

f =

and

The time select inputs (A and B) provide a two–bit address

when B is “0”, normal counting is interrupted and the 9th

counter stage receives its clock directly from the oscillator

The Q/Q select output control pin provides for a choice of

output level. When the counter is in a reset condition and

Q/Q select pin is set to a “0” the Q output is a “0”,

correspondingly when Q/Q select pin is set to a “1” the Q

output is a “1”.

When the mode control pin is set to a “1”, the selected

count is continually transmitted to the output. But, with

Expanded Block Diagram) resets, counting commences,

output will not change. Thus, a Master Reset pulse must be

applied or a change in the mode pin level is required to reset

the single cycle operation.

DIGITAL TIMER APPLICATION

NC

AR

MR

INPUT

B

A

N.C.

OUTPUT

MODE

Q/Q

1

2

3

4

5

6

78

9

10

11

12

13

14

When Master Reset (MR) receives a positive pulse, the

internal counters and latch are reset. The Q output goes high

and remains high until the selected (via A and B) number of

clock pulses are counted, the Q output then goes low and

remains low until another input pulse is received.

This “one shot” is fully retriggerable and as accurate as the

input frequency. An external clock can be used (pin 3 is the

clock input, pins 1 and 2 are outputs) if additional accuracy

is needed.

Notice that a setup time equal to the desired pulse width

output is required immediately following initial power up,

during which time Q output will be high.