Counters 2.1

MSI Counters

Counter ICs

©Paul GodinUpdated Aug 2013prgodin @ gmail.com

Counters 2.2

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 vendor-specific. An example is the chip in a TI Calculator.

Counters 2.3

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:

• Up/Down selection input• Dual clock inputs (one for up, one for down)

• Frequency division:• 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 2.4

The 7490• The 7490 is a decade counter (Modulus = 10)

• List the features for the 7490:

Counters 2.5

7490 Frequency Division• The 7490 has two modes of operation:

• Mod-10 up count• Symmetrical divide-by-ten• Bi-Quinary frequency division

Counters 2.6

The 74192• The 74192 is a decade counter (Modulus = 10)

• List the features for the 74192:

Counters 2.7

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 2.8

The 14518• The 14518 (or 4518) is a decade counter (Mod = 10)

• List the features for the 14518:

Counters 2.9

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 2.10

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 2.11

MSB Edge

Decade

D C B A0 0 0 00 0 0 10 0 1 00 0 1 10 1 0 00 1 0 10 1 1 00 1 1 11 0 0 01 0 0 1

A

B

C

D

LSB

MSB

Negative edge produced by 9-to-0 transition on D

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:

Counters 2.12

÷16 ÷16 ÷16 ÷832768Hz

2048Hz128Hz

8Hz1Hz

How many flip-flops if we built this as a single counter?

Counters 2.13

MSB Edge Cascading

Decade

D C B A0 0 0 00 0 0 10 0 1 00 0 1 10 1 0 00 1 0 10 1 1 00 1 1 11 0 0 01 0 0 1

Mod-6

D C B A0 0 0 00 0 0 10 0 1 00 0 1 10 1 0 00 1 0 1

Negative edge produced by 5-to-0 transition on C

D does not change so it isn’t used for cascade

Decade

LSB

MSB

Counters 2.14

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 2.15

End

©Paul R. Godinprgodin @ gmail.com