CSC 3650 Introduction to Computer Architecture Time: 3:30 to 6:30 Meeting Days: W Location: Oxendine 1237B Textbook: Essentials of Computer Architecture, Author: Douglas E. Comer, 2005, Pearson Prentice Hall Spring 2011 Chapter Seven CPUs: Microcode, Protection, and Processor Modes Dr. Chuck Lillie
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CSC 3650 Introduction to Computer Architecture Time: 3:30 to 6:30Meeting Days: WLocation: Oxendine 1237B Textbook: Essentials of Computer Architecture,
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CSC 3650 Introduction to Computer Architecture
Time: 3:30 to 6:30 Meeting Days: W Location: Oxendine 1237B
Textbook: Essentials of Computer Architecture, Author: Douglas E. Comer, 2005, Pearson Prentice Hall
Spring 2011
Chapter SevenCPUs: Microcode, Protection, and
Processor Modes
Dr. Chuck Lillie
Instruction Code Formats
opcode operands
OpcodesAdd = 1010Move = 1000Load = 0000Store = 0001Push B = 0101Push C = 0110Pop A = 1100
Less complex with fewer operands, but more difficult to program
Instruction Set Architecture (ISA) Design
• What should the ISA and its processor be able to do?– Completeness: does the instruction set hall all the instructions a
program needs to perform its required tasks• PC needs rich set
• Microwave oven needs limited set
– Orthogonality: no overlap of instructions• Minimize overlap – provides necessary functions with minimum instructions
– Register set: more registers speeds up CPU operations, but unused registers take up needed space
• Does the processor have to be backward compatible with others?
• What types and size of data will microprocessor deal with?– Need floating point instructions?
– Need character instructions?
– Are interrupts necessary?
– Are conditional instructions necessary?
A Relatively Simple Instruction Set Architecture
• Memory Module– 64K (= 216) bytes of memory with each byte having 8 bits (64K X
8)
– I/O is treated as memory access (Memory Mapped I/O)
• 3 Registers– Accumulator AC
• 8 bit register used as on of the operands
• Data loaded from memory to AC and AC to memory
– R• 8 bit general purpose register
– 1-bit zero flag Z• Set when arithmetic or logic instruction is executed
• 0 results sets flag to 1
Instruction Set for Relatively Simple CPU
• Γ = 16 bit memory address• An instruction with a memory reference requires 3-bytes• Instruction with 3-bytes stores address bytes with low order bytes first and high order bytes next