MSI Counters
Counter ICs
©Paul Godin
Updated Aug 2013
Counters
prgodin @ gmail.com
2.1
Introduction
• SSI: Small Scale Integration. Usually refers to IC’s that
contain individual gates or flip-flops.
• MSI: Medium Scale Integration. Usually refers to IC’s
that contain counters, encoders, etc…
• LSI and VLSI: Large and Very Large Scale Integration.
Refers to IC’s that can perform large logic functions,
such as CPLDs, microprocessors, etc.
• ASIC: Application Specific IC. Refers to IC’s that are
custom built for specific functions, and are vendorspecific. An example is the chip in a TI Calculator.
Counters 2.2
Counter ICs
•
There are many counter ICs available, each with a
specific set of functions. Examples of functions
include:
•
•
Loading a value (instead of resetting to 0)
Counting up or down by either:
•
•
•
Frequency division:
•
•
•
•
•
Up/Down selection input
Dual clock inputs (one for up, one for down)
Specific input frequencies (i.e. ÷ 60 or by a crystal
frequency)
Output patterns
Multiple counters within a single package
Decade or binary counting
Borrow and Carry,...
Counters 2.3
The 7490
•
The 7490 is a decade counter (Modulus = 10)
•
List the features for the 7490:
Counters 2.4
7490 Frequency Division
•
The 7490 has two modes of operation:
•
•
•
Mod-10 up count
Symmetrical divide-by-ten
Bi-Quinary frequency division
Counters 2.5
The 74192
•
The 74192 is a decade counter (Modulus = 10)
•
List the features for the 74192:
Counters 2.6
The 74192
•
The 74192 has several features.
•
Note the specification sheet does not include a
function table, but uses a sample timing diagram to
explain the functions of the device.
Counters 2.7
The 14518
•
The 14518 (or 4518) is a decade counter (Mod = 10)
•
List the features for the 14518:
Counters 2.8
The 14518
•
The 14518 is a popular counter IC because it
includes two decade counters within a monolithic
package.
•
Note that this device is electrically different from
the 74xxx series of devices.
•
This device can be configured to accept either a
positive edge or a negative edge.
Counters 2.9
Cascading Counters
•
Cascading means connecting one device to another
device for it to continue the logic operation.
•
When designing a digital clock, counters need to be
cascaded.
•
Consideration must be given to how the next
counter in the cascade will be incremented.
•
The MSB that changes will produce a negative edge
when the count returns to zero.
Counters 2.10
MSB Edge
Decade
D
C
B A
0
0
0 0
0
0
0 1
0
0
1 0
0
0
1 1
0
1
0 0
0
1
0 1
0
1
1 0
0
1
1 1
1
0
0 0
1
0
0 1
A
LSB
B
C
MSB
D
Negative edge produced by
9-to-0 transition on D
Counters 2.11
Frequency Division
•
Counters are often used as frequency dividers.
•
Example: A common frequency for crystal oscillators is
32.768 KHz. We can divide this frequency into a 1 Hz
pulse by using full-sequence counters:
32768Hz
÷16
÷16
2048Hz
÷16
128Hz
÷8
8Hz
1Hz
How many flip-flops if we built this as a single counter?
Counters 2.12
MSB Edge Cascading
Decade
Mod-6
D
C
B A
D
C
B A
0
0
0 0
0
0
0 0
0
0
0 1
0
0
0 1
0
0
1 0
0
0
1 0
0
0
1 1
0
0
1 1
0
1
0 0
0
1
0 0
0
1
0 1
0
1
0 1
0
1
1 0
0
1
1 1
1
0
0 0
1
0
0 1
Decade
LSB
MSB
Negative edge produced by
5-to-0 transition on C
D does not change so it
isn’t used for cascade
Counters 2.13
In-Class Exercise
•
Use EWB to design a 12 hour clock with AM and PM
settings. Include seconds, minutes and hours.
•
Use the appropriate counter IC for this exercise.
•
Use EWB Sub-Circuits.
•
Special consideration to the hours:
•
•
The clock counts from 12 to 1
Consider what state must be detected and what must
happen.
Counters 2.14
End
©Paul R. Godin
prgodin @ gmail.com
Counters 2.15