MSI Counters

Counter ICs

©Paul Godin

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 2.2

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: • 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 2.3

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

LSB MSB

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 ÷16 ÷8 2048Hz 128Hz 8Hz 1Hz How many flip-flops if we built this as a single counter?

Counters 2.12

MSB Edge Cascading

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 Mod-6 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

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