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PDF LM2240 Data sheet ( Hoja de datos )
| Número de pieza | LM2240 | |
| Descripción | Programmable Timer/Counter | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM2240 (archivo pdf) en la parte inferior de esta página. Total 10 Páginas | ||
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www.DataSheet4U.com
August 1990
LM2240
Programmable Timer Counter
General Description
The LM2240 Programmable Timer Counter is a monolithic
controller capable of both monostable and astable opera-
tion Monostable operation allows accurate microsecond to
five day time delays Long delays up to three years can
easily be generated by cascading two timers The timer con-
sists of a time-base oscillator programmable 8-bit counter
and control flip-flop An external resistor-capacitor (RC) net-
work sets the oscillator frequency and allows delay times
from 1 RC to 255 RC to be selected In the astable mode of
operation a single RC network sets the base frequency
The frequencies of the squarewaves at the 8 outputs are
each at different factors of 2 from the base frequency If 2 or
more of the outputs are shorted together various pulse pat-
terns can be generated These frequencies or pulse pat-
terns can also easily be synchronized to an external signal
The trigger reset and outputs are all TTL and CMOS com-
patible for easy interface with digital systems The timer’s
high accuracy and versatility in producing a wide range of
time delays makes it ideal as a direct replacement for me-
chanical or electromechanical devices
Features
Y Accurate timing from microseconds to days
Y Programmable delays from 1 RC to 255 RC
Y TTL and CMOS compatible outputs
Y Timing directly proportional to RC time constant
Y High accuracy
Y External sync and modulation capability
Y Wide supply voltage range
Y Excellent supply voltage rejection
Connection Diagram
16-Lead Molded DIP
Top View
See NS Package Number N16E
Order Number LM2240N
TL H 10837 – 1
C1995 National Semiconductor Corporation TL H 10837
RRD-B30M115 Printed in U S A
1 page  
Functional Description
TL H 10837 – 4
VCC e Pin 16
GND e Pin 9
FIGURE 1 Logic Symbol
When power is applied to the LM2240 with no trigger or
reset inputs activated the circuit starts with all outputs
HIGH Application of a positive going trigger pulse to the
trigger pin initiates the timing cycle The trigger input acti-
vates the time-base oscillator enables the counter section
and sets the counter outputs LOW The time-base oscillator
generates timing pulses with a period T e 1 RC this is the
period of the waveform appearing at pin 14 These clock
pulses are counted by the binary counter section The tim-
ing sequence is completed when a positive going reset
pulse is applied to the Reset pin
Once triggered the circuit is immune from additional trigger
inputs until the timing cycle is completed or a reset input is
applied If both the reset and trigger are activated simulta-
neously the trigger takes precedence
Figure 2 gives the timing sequence of output waveforms at
various circuit terminals subsequent to a trigger input
When the circuit is in a reset state both the time-base and
the counter sections are disabled and all the counter out-
puts are HIGH
TL H 10837 – 5
FIGURE 2 Timing Diagram of Output Waveforms
In monostable applications one or more of the counter out-
puts are connected to the reset terminal with S1 closed
(Figure 3) The circuit starts timing when a trigger is applied
and automatically resets itself to complete the timing cycle
when a programmed count is completed Each of the vari-
ous multiplies of T shown at the LM2240’s outputs in Figure
3 represent the duration of time after a trigger pulse that
that particular output is low (it’s not the period of the wave-
form) if the output is not tied to any other outputs TO repre-
sents the duration of time that the circuit output which is the
common point of all the counter outputs which are shorted
together is low If none of the counter outputs are connect-
ed back to the reset terminal (switch S1 open) the circuit
operates in an astable or free running mode following a
trigger input
TL H 10837 – 6
FIGURE 3 Basic Circuit Connection
for Timing Applications
(Monostable S1 Closed Astable S1 Open)
Important Operating Information
Ground connection is pin 9
Reset (R) (pin 10) sets all outputs HIGH
Trigger (TRIG) (pin 11) sets all outputs LOW
Time-base output (TBO) (pin 14) can be disabled by bring-
ing the RC input (pin 13) LOW via a 1 0 kX resistor
Normal TBO (pin 14) is a negative going pulse greater than
500 ns
NOTE Under the conditions of high supply voltages (VCC l 7 0V) and low
values of timing capacitor (CT k 0 1 mF) the pulse width of TBO
may be too narrow to trigger the counter section This can be cor-
rected by connecting a 600 pF capacitor from TBO (pin 14) to
ground (pin 9)
Reset (pin 10) stops the time-base oscillator
Outputs (O0
VOL s 0 4V
O128) (pins 1 – 8) sink 2 0 mA current with
For use with external clock minimum clock pulse amplitude
should be 3 0V with greater than 1 0 ms pulse duration
5
5 Page | ||
| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet LM2240.PDF ] | |
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