Objective of this lab:

	To study the operation of an 8-bit CPU and control unit. 

Preparation

	Read lab lecture notes and the material in this page.

Lab Assignments

1. Obtain an 8-bit CPU working circuit file

   
          ~ftp/pub/class/301/ftp/8bitcpu.cct
   
   

   
   The circuit just obtained is a 8 bit version of the 1 bit CPU we built in last lab with a few additions:
   • there is now a 256 x 8 bit memory attached to the bus through a Memory Address Register(MAR)
   • there is now a Program Counter(PC) with a built in increment by one function.
   • the ALU has been expanded to perform the invert operation on the Accumulator(ACC)
   • all the switches have been grouped into one area to simulate a control unit.

   
   	To get a feel for the circuit before more details are examined, 
   	do the following: 
       
   	1.	load the number 8 into memory location 2 
   
   	2.	move (the contents in) memory location 2 to the PC 
   
   	3.	increment the PC 
         
          
         Write down the signals with the microinstructions to hand-in:
   
           ________________________________
   
           ________________________________
   
           ________________________________
   
           ________________________________
   
   

2. Execute the program (Hand in)

   
   a).	Write out the equivalent assembly language mnemonics of the following 
   	machine language code:
     
   	
   
         Location 	Contents 	Assembly Language Mnemonics 
         =============================================================
         0 	10000001  
         -------------------------------------------------------------
         1 	00010110  
         -------------------------------------------------------------
         2 	00000101  
         -------------------------------------------------------------
         3 	00001000  
         -------------------------------------------------------------
   
   	
   
   b).	Load the preceding program (in machine code) to the memory. 
   
   c).     Pre-load value 1 in the B register, preload 0 in the memory location 8. 
           Make sure the PC points to the beginning of the program. 
   
   d).  	Write out the microinstructions necessary to execute the program. 
   
           Hand in the procedures used in the different steps including
   	the equivalent assembly language mnemonics and
   	microinstructions needed to execute the program.
           ALSO remember to hand in the answers to the following two questions.
   
   

3. Add OR operation to the 8-bit CPU that we have learned.

   
           opcode# MNEMONIC                 DESCRIPTION
           ==============================================================
           00      XOR source, destination  XOR the contents of source,
                                            destination, and store the
                                            result in the destination
           --------------------------------------------------------------
           01      AND source, destination  AND the contents of source,
                                            destination, and store the
                                            result in the destination
           --------------------------------------------------------------
           10      NOT source, destination  invert the contents of
                                            source and store the result
                                            in destination
           --------------------------------------------------------------
           11      OR source, destination   OR the contents of source,
                                            destination,  and store the
                                            result in destination
           --------------------------------------------------------------
   
   
   

   Please note that the ALU will need two 8-bit operands input and produce the output of the ALU.
   Hand in a screen shot showing your new ALU in the 8-bit CPU circuit.

4. Implement the following tasks with your enhanced 8-bit CPU, remember to pre-load the registers or memory when needed:

   
           1) Write out and hand in the microinstructions to perform this operation
   
              XOR #5,(C)
              including the machine code and how you load it to the memory.
   
              Pre-load the registers or memory when needed.
              For example:  Load 00001000  to the C register
                            Load 00000000  to the memory location 8
   
           2) Write out and hand in the microinstructions to perform the operation
   
              OR 5, 8
              including the machine code and how you load it to the memory.
   
              Pre-load the registers or memory when needed.
              For example:  Load 00000000  to the memory location 5
                            Load 00001010  to the memory location 8
   
           

Questions (hand in the answers)

 
	1) Describe the purpose of the 3->8 decoder. 

	2) Describe how the RAM chip control signals are used to read 
	   and write to memory.