1. Digital Design
Jeff Kautzer
Univ Wis Milw

2. Review of Medium Scale Integration (MSI) Logic Circuits
Common digital system tasks are commercially available as MSI logic devices in many different TTL and CMOS families
Functions such as decoding/encoding, multiplexing, demultiplexing, comparison, arithmetic, code converting, and data busing

3. De-Multiplexers
A Demultiplexer (DEMUX) takes a single input & distributes it over several outputs.

4. 1-line-to-8-line demux

5. 74138 style decoder can function as a demultiplexer with E1 used as the data input. Typical waveforms shown for a select code of A2 A 1 A 0 = 000 show that O0 is identical to the data input I on E1.

6. Security monitoring system MUX/DEMUX Application

7. Synchronous data transmission system

8. One 16 bit transmission cycle

9. 74HC85 4-bit magnitude comparator
Comparators
A Comparator takes two inputs numbers and yields a result to indicate <, =, >
74HC85 4-bit magnitude comparator

10. 74HC85 wired as a single 4-bit comparator
Two 74HC85s cascaded to perform an 8-bit comparison

11. Magnitude comparator used in a simple controller application
Set Point
Magnitude comparator used in a simple controller application

12. Basic idea of a two-digit BCD(hex)-to-binary converter.
Code Converters
A code converter changes data presented in one type of binary code to another type of binary code
Basic idea of a two-digit BCD(hex)-to-binary converter.

13. BCD-to-binary Conversion
Compute the binary sum of the binary equivalents of all bits in the BCD representation that are 1s.
Example
(BCD)
= (2) (10) (40)
= (52)

14. BCD-to-binary converter with 74HC83 4-bit parallel adders.

15. Data Bus Interface
These circuits include tristate-able buffers and latches
Time Division Multiplexing
3 different devices can transmit 8-bit data over an 8-line data bus to a µ-processor; only one device at a time is enabled so that bus contention is avoided.

16. Truth table and logic diagram for the 74ALS173 tristate register

17. Tristate registers connected to a data bus.

18. Signal activity during the transfer of the data 1011 from register A to register C

19. Simplified way to show signal activity on data bus lines.

20. Simplified representation of bus arrangement.

21. Bundle method for simplified representation of data bus connections
Bundle method for simplified representation of data bus connections. The “/8” denotes an 8 bit data bus.