CSE370 Laboratory Assignment 4

Making a Full Adder with a Multiplexer, Decoder, and PAL (Programmable Array Logic)

Distributed: Monday, January 30, 2006
Due: end of lab period


In this laboratory assignment you will learn to use multiplexers, decoders, and PALs to create a full adder. 

The PAL (Programmable Array Logic) we will be using in this class is called the 22V10 (here is the functional logic diagram). This is a very flexible PAL that you will be using in different ways this quarter. At the core of this PAL are 10 logic blocks that each computes a Boolean function. This output can either go straight to a pin or through a register to a pin. We are concerned only with combinational logic right now, so we will ignore the register. The output also feeds back into the PAL, so that you can use it to implement multi-level logic functions.

This is how this PAL gets its name: functions of up to 22 inputs, with 10 distinct outputs, hence, 22V10.  Note: for now, ignore the other logic elements in this PAL, we'll come back to them later in the quarter.  After you familiarize yourself with the component, you will write some Verilog code that will be compiled into the logic in this PAL. This is yet another useful capability of the ActiveHDL tool. We'll use the full-adder circuit from the previous lab assignment as the example.  You will then "program" the PAL and use it on your protoboard.

Modules you will use from previous labs:

  1. Your verilog implementation of a full adder from Lab #3
  2. The verilog full adder test fixture (FA_tf.v) from Tutorial # 3 in Lab #3

For the Active-HDL schematics in the lab, use only the c74XXX chip packages in the lib370 library. The following figure shows how to wire in Vcc and GND signals in Active-HDL.


Part 1 (May be completed before Lab)

  1. Use a 3:8 decoder (the '138 chip) and gates to implement a full adder with the c74XX packages in the lib370 library. These chips are identical to the real chips in your kit.  Remember to use de Morgan's law to pick the right packages.  Create a test circuit schematic using the test fixture given in the tutorial to test your design. As you design your circuit, be sure to use the chip maps as a guide, and pay close attention to the "enable" semantics on the decoder chip. (NOTE: You do not need to hand in your testing block diagram) 
  2. You can also implement a full-adder using multiplexers.  Use one standard 4:1 multiplexer ('153) for each output (sum and carry-out), along with inverters as necessary, to implement a full-adder. Note that the '153 chip actually contains two independent multiplexers, so you only need one of these chips total. Do not use the 'mux4' part in lib370; use 'c74153.'  Create a test circuit schematic withe the full adder test ficture to verify your design. Again, pay attention to the enable semantics for the '153.. (NOTE: You do not need to hand in your testing block diagram) 
  3. Spend some time familiarizing yourself with the 22V10 functional logic diagram.  Make sure you see how logic functions are computed in this component.

Part 2

  1. Complete the entire PAL tutorial that explains how to compile a circuit into a PAL using ActiveHDL and the Cypress compiler. Now compile your full-adder Verilog module (from the previous lab) and then program it into a PAL using the PAL "programmer". You should already have the Verilog file for this circuit and have verified it using the simulator. The PAL is the long chip with the image of a tree on it, and you should already have 2-3 of them in your kit.
  2. After you've programmed your PAL, place it in your circuit board and wire its inputs and outputs to some switches and LEDs, respectively. Use SW1 for A, SW2 for B, and SW3 for Cin and LED1 for the Sum and LED2 for the Cout. Verify that the full adder operates correctly. Make sure you leave room for the multiplexer and decoder chips on the breadboard.  In addition, you should make sure to review the reports generated by the compilation process and understand what equations were generated to be implemented by the PAL.  The TAs may ask you about this, so be sure to review it carefully.
  3. Wire up your multiplexor implementation of your full adder using the same switches for A, B and Cout as the PAL but use LED3 for the Sum and LED4 for the Cout. 
  4. Demonstrate the two implementations of a full adder to a TA.



 Lab Demonstration/Turn-in Requirements: A TA will "check you off" after you:

  1. Show your decoder implementation using c74XXX gates in Active-HDL to a TA.
  2. Show  your multiplexer implementation using c74XXX gates in Active-HDL to a TA.
  3. Demonstrate both the PAL and multiplexer implementations on your prototyping board.


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