1. Counters 2.1 MSI Counters Counter ICs ©Paul Godin Updated Aug 2013 prgodin @ gmail.com

2. 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.

3. 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,...

4. Counters 2.4 The 7490 The 7490 is a decade counter (Modulus = 10) List the features for the 7490:

5. 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

6. Counters 2.6 The 74192 The 74192 is a decade counter (Modulus = 10) List the features for the 74192:

7. 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.

8. Counters 2.8 The 14518 The 14518 (or 4518) is a decade counter (Mod = 10) List the features for the 14518:

9. 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.

10. 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.

11. Counters 2.11 MSB Edge Decade DCBA 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 A B C D LSB MSB Negative edge produced by 9-to-0 transition on D

12. 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 ÷8 32768Hz 2048Hz 128Hz 8Hz 1Hz How many flip-flops if we built this as a single counter?

13. Counters 2.13 MSB Edge Cascading Decade DCBA 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 Mod-6 DCBA 0000 0001 0010 0011 0100 0101 Negative edge produced by 5-to-0 transition on C D does not change so it isn’t used for cascade Decade LSB MSB

14. 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.

15. Counters 2.15 End ©Paul R. Godin prgodin @ gmail.com