EE 231
Prelab 6: Microprocessor Address Decoding using Demultiplexers

1. How many inputs/outputs does the address decoder have?

   
   
   
   

2. Complete the truth table for the R' and W' outputs.
   

   R/W'	E		R'	W'

   
   and thus derive the expression for:
   R' =
   W' =

3. What device is the 74HC138A ?

   
   
   

4. Make a table showing the address ranges which will select the specific devices for your address decoder (use a separate sheet of paper).
5. Which signals do we need to address all of the proposed devices in Lab 6 uniquely ?
   
   
   Conversely, which lines can you safely ignore?

   
   
   

6. Which address line remains constant when selecting any of the seven devices?

   
   

7. How many chip select (CS) bits does a 74HC138 have?
   
   Does this give you any ideas as to how you might use the E signal and the constant address line?

   
   
   

8. Design an address decoder to implement the functions required in the Lab. Sketch your design including as much detail so as to be able to begin building it when arriving at the lab.