Learn an 8-Bit CPU

1. Purpose

CPU is the most important part of a computer. It is controlled by a series of small operations called microoperations. You have got a feel in the last lab with a one-bit and a two-bit CPU. In this lab, we will look at an 8-bit CPU and see how it works.

2. Explanations:

1. The difference between absolute vs immediate addressing
   • In absolute addressing, the operand is located in the address specified in the instruction.
     For example: NOT 2,B means NOT (or invert) the contents of location 2, and save it in register B.
   • In immediate addressing, the operand is specified in the instruction.
     For example: AND #2,B means AND the value 2, with register B and save the result in B.
2. Students should copy the file: ~ftp/pub/class/301/8bitcpu.cct.
   This circuit is simply an extension of what they have already done.
   Notice the similarities e.g. temp, accumulator, IR, B and C registers, and the external input.
3. Notice the differences, for example, the memory has a memory address register,
   there is a decoder associated with the ALU, and there is a PC and an adder to produce a PC+1 value.

3. CONCLUSION

 
Many devices may be connected to a common bus by using tri-state buffers. 

4. Lab Assignments

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Copyright: Department of Computer Science, University of Regina.