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Fairchild Semiconductor
Fairchild Semiconductor

MM74C928 Datasheet

4-Digit Counters

MM74C928 Datasheet Preview

October 1987
Revised January 1999
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.
s Wide supply voltage range: 3V to 6V
s Guaranteed noise margin: 1V
s High noise immunity: 0.45 VCC (typ.)
s High segment sourcing current: 40 mA
@ VCC 1.6V, VCC = 5V
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-
The input protection circuitry consists of a series resistor,
and a diode to ground. Thus input signals exceeding VCC
will not be clamped. This input signal should not be allowed
to exceed 15V.
Ordering Code:
Order Number
Package Number
Package Description
16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300” Wide
18-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300” Wide
18-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300” Wide
18-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300” Wide
© 1999 Fairchild Semiconductor Corporation DS005919.prf
Page 1

Connection Diagrams
Pin Assignments for DIP
Top View
Functional Description
— Asynchronous, active high
Display Select — High, displays output of counter
Low, displays output of latch
Latch Enable — High, flow through condition
Low, latch condition
—Negative edge sensitive
Logic Diagrams
Top View
MM74C926, MM74C927, MM74C928
Segment Output — Current sourcing with 40 mA @VOUT =
VCC 1.6V (typ.) Also, sink capability = 2
LTTL loads
Digit Output — Current sourcing with 1 mA @VOUT =
1.75V. Also, sink capability = 2 LTTL loads
Carry-Out — 2 LTTL loads. See carry-out waveforms.
Page 2

Logic Diagrams (Continued)
Page 3
Part Number MM74C928
Manufactur Fairchild Semiconductor
Description 4-Digit Counters
Total Page 9 Pages
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MM74C922 , MM74C922 , MM74C923 , MM74C923 , MM74C923 , MM74C925 , MM74C925 , MM74C926 , MM74C926 , MM74C927 , MM74C927 , MM74C928 , MM74C928 ,

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