Document
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 internal output latch NPN output sourcing drivers for a 7-segment 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 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 significant 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 VCC (typ ) 40 mA VCC b 1 6V VCC e 5V
Y
Design Considerations
Segment resistors are desirable to minimize power dissipation 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 VCC 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 – 1
TL F 5919 – 2
Top View Order Number MM74C925
Top View Order Number MM74C926 MM74C927 or MM74C928
C1995 National Semiconductor Corporation
TL F 5919
RRD-B30M105 Printed in U S A
Absolute Maximum Ratings (Note 1)
If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Distributors for availability and specifications .