1. Unit 9 Multiplexers, Decoders, and Programmable Logic Devices
Fundamentals of Logic Design by Roth and Kinney

2. 9.1 Introduction SSI—small scale integration
NAND,NOR,AND, and OR, inverters, and flip-flops (1-4 gates, 6 inverters, 1 or 2 flip-flops); in a single pkg
MSI—medium-scale integration
Adders, Multiplexers, Decoders, Registers, and Counters( gates—in a single package)
LSI—large –scale integration (memories or microprocessors) (100-few thousand gates; in a single package)
VLSI—very large scale integration (memories or microprocessors) (several thousand gates or more in a single package).

3. 9.1 (cont.)
Cost tends to decrease when LSI and VLSI circuits are used (wiring, mounting, and maintaining designs.)
Design trends—LSI and VLSI.

4. 9.2 Multiplexers Data inputs and control inputs.
The control inputs are used to select one of the data inputs.
See Figures 9-1 and 9-2.
Note that the output Z of the 4 x 1 multiplexer is Z= A’B’I0 + AB’I1 +AB’I2 + ABI3

5. 9.2 (cont.) Equation 9-2 –shows output Z for an 8x1 multiplexer.
Figure 9.3—Logic diagram for 8 to 1 Mux.
NAND or NOR gates can be used .
2-levels shown
Figure 9-4—Multi-Level 8 to 1 Mux using NANDS.
Figure 9-9 illustrates the MUX used to implement a simple function.

6. 9.3 Three-State Buffers
A simple buffer can be used to increase the driving capability of a gate output.
See Figure 9.10, page 266.
A three-state (tri-state) buffer allows the outputs of two or more gates to be connected together.
See Figure 9-11; when the control “B” is 0 the output will have a high inpedence.

7. 9.4 Decoders and Encoders Figure 9-17 3-5o-8 line decoder
Generates all of the minterms.
Only one output will be high for each combination of the input variables.

8. 9.4 (cont.) Figure 9-18 A 4 –to- 10 line decoder (7442)
(a) Logic diagram
(b) Block diagram
(c) Truth Table (one output will be a 0)
Binary coded decimal are used as the input.

9. 9.4 (cont.)
An encoder performs the inverse function of a decoder (Figure 9.20).

10. 9.5 Read-Only Memories ROM—read only memory; used to store data.
Figure 9-21 – An 8-word x 4 bit ROM.
(a) Block Diagram
(b) Truth Table

11. 9.6 Programmable Logic Devices
PLD—programmable logic device– a digital integrated circuit capable of being programmed to provide a variety of different logic functions.
PLA—programmable logic array
Similar in function to a ROM

12. 9.7 Complex Programmable Logic Devices
CPLD—many PLAs can be placed today on a single chip.
Figure 9-34—Architecture of Xilinx XCF3064XL CPLD.

13. 9.8 Field-Programmable Gate Arrays
FPGA—an IC that contains an array of identical logic cells (configurable logic blocks) with programmable interconnections. (See Figure 9-36)
Array of CLBs is surrounded by I/O blocks.
The I/O blocks connect the CLBs with the pins of the FPGA chip.
The space between CLBs is used to route the connections between the CLB outputs and inputs.

14. 9.8 (cont.) Simplified CLB—Figure 9-37
2 “function generators” of logic lookup Tables (LUTs)
LUTs—reprogrammable ROMs (16 1-bit words
LUTs—store the truth table of the function being implemented.
2 flip-flops ( outputs XQ and YQ)
Multiplexors (for routing signals)
H chooses between F and G.
Selects combinational logic outputs, X and Y.