TLF5919

March 1988

MM74C925 MM74C926 MM74C927 MM74C928

4-Digit Counters with Multiplexed

7-Segment Output Drivers

General Description

These CMOS counters consist of a 4-digit counter an inter-

nal output latch NPN output sourcing drivers for a 7-seg-

ment display and an internal multiplexing circuitry with four

multiplexing outputs The multiplexing circuit has its own

free-running oscillator and requires no external clock The

counters advance on negative edge of clock A high signal

on the Reset input will reset the counter to zero and reset

the carry-out low A low signal on the Latch Enable input will

latch the number in the counters into the internal output

latches A high signal on Display Select input will select the

number in the counter to be displayed a low level signal on

the Display Select will select the number in the output latch

to be displayed

The MM74C925 is a 4-decade counter and has Latch En-

able Clock and Reset inputs

The MM74C926 is like the MM74C925 except that it has a

display select and a carry-out used for cascading counters

The carry-out signal goes high at 6000 goes back low at

0000

The MM74C927 is like the MM74C926 except the second

most significant digit divides by 6 rather than 10 Thus if the

clock input frequency is 10 Hz the display would read

tenths of seconds and minutes (ie 9599)

The MM74C928 is like the MM74C926 except the most sig-

nificant digit divides by 2 rather than 10 and the carry-out is

an overflow indicator which is high at 2000 and it goes back

low only when the counter is reset Thus this is a 3

-digit

counter

Features

Y

Wide supply voltage range

3V to 6V

Y

Guaranteed noise margin

1V

Y

High noise immunity

Y

High segment sourcing current

40 mA

Y

Internal multiplexing circuitry

Design Considerations

Segment resistors are desirable to minimize power dissipa-

tion and chip heating The DS75492 serves as a good digit

driver when it is desired to drive bright displays When using

this driver with a 5V supply at room temperature the display

can be driven without segment resistors to full illumination

The user must use caution in this mode however to prevent

overheating of the device by using too high a supply voltage

or by operating at high ambient temperatures

The input protection circuitry consists of a series resistor

will not be clamped This input signal should not be allowed

to exceed 15V

Connection Diagrams

Dual-In-Line Package

TLF5919 – 1

Top View

Order Number MM74C925

Dual-In-Line Package

TLF5919 – 2

Top View

Order Number MM74C926

MM74C927 or MM74C928

C1995 National Semiconductor Corporation

RRD-B30M105Printed in U S A