MM74C925 MM74C926 MM74C927 MM74C928 4-Digit Counters
with Multiplexed 7-Segment Output Drivers
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 (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 3 -digit
counter
Features
Y
Y
Y
Y
Wide supply voltage range
Guaranteed noise margin
High noise immunity
High segment sourcing current
Internal multiplexing circuitry
3V to 6V
1V
0 45 V
CC
(typ )
40 mA
V
CC
b
1 6V V
CC
e
5V
Y
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
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
Connection Diagrams
Dual-In-Line Package
Dual-In-Line Package
TL F 5919 鈥?1
TL F 5919 鈥?2
Top View
Order Number MM74C925
Top View
Order Number MM74C926
MM74C927 or MM74C928
C
1995 National Semiconductor Corporation
TL F 5919
RRD-B30M105 Printed in U S A
1
2
3
4
5
6
7
8
