October 1987
Revised January 1999
MM74C925 • MM74C926 • MM74C927 • MM74C928 4-Digit Counters with Multiplexed 7-Segment Output Drivers
© 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
■ Wide supply voltage range: 3V to 6V
■ Guaranteed noise margin: 1V
■ High noise immunity: 0.45 V
CC
(typ.)
■ High segment sourcing current: 40 mA
@ V
CC
− 1.6V, V
CC
= 5V
■ 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,
and a diode to ground. Thus input signals exceeding V
CC
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
