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Digital Design

Explore the functionalities of MSI logic devices such as demultiplexers, comparators, code converters, and data bus interfaces. Learn about applications in security monitoring, synchronous data transmission, and more.

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Digital Design

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  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 A1 A0 = 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. 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. Set Point Magnitude comparator used in a simple controller application

  12. 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 01010010(BCD) = 0000010 (2) + 001010 (10) + 0101000 (40) = 0110100 (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. The “/8” denotes an 8 bit data bus.

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