October 1987

Revised January 1999

© 1999 Fairchild Semiconductor Corporation

DS005919.prf

www.fairchildsemi.com

MM74C925 • MM74C926 • MM74C927 • MM74C928

4-Digit Counters with Multiplexed

7-Segment Output Drivers

General Description

The MM74C925, MM74C926, MM74C927 and MM74C928

CMOS counters consist of a 4-digit counter, an internal out-

put latch, NPN output sourcing drivers for a 7-segment dis-

play, 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 sig-

nal 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

Enable, 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 (i.e., 9:59.9).

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

3½-digit counter.

Features

s Wide supply voltage range:

3V to 6V

s Guaranteed noise margin: 1V

s High segment sourcing current: 40 mA

s 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 illu-

mination. 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 tempera-

tures.

The input protection circuitry consists of a series resistor,

will not be clamped. This input signal should not be allowed

to exceed 15V.

Ordering Code:

Order Number

Package Number

Package Description

MM74C925N

N16E

16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300” Wide

MM74C926N

N18A

18-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300” Wide

MM74C927N

N18A

18-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300” Wide

MM74C928N

N18A

18-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300” Wide