Midterm Wednesday Chapter 1-3: Number /character representation and conversion Number arithmetic Combinational logic elements and design (DeMorgan’s Law) Sequential logic elements and design (State machines) Memory organization and implementation Clocks and timing

Overview The von Neumann Machine - The programmable digital computer (both program and data are stored in the computer memory) - Computer comprised of: processing unit, memory, control unit, input(s), and output(s) Introducing the LC-3 Computer - A “toy” computer for us to learn from: 16 bit machine, word addressable, 64K or 65,536 locations (Could it have an address space of 1 Gig? 1 Gig needs 30 bits of addressing) Computer Machine Instructions – Computer “native” instructions - The basic instructions that all programs use on that computer (The “atomic” unit of work done by a computer) The Instruction Cycle - The steps in the execution of a machine language instruction (Fetch, Decode, Evaluate Address(es), Fetch operand(s), Execute, and store results)

The LC-3 Computer a von Neumann machine

From Logic to Data Path Data Paths The data path of a computer is all the logic used to process information. –See the data path of the LC-3 on next slide. Combinational Logic –Decoders -- convert instructions into control signals –Multiplexers -- select inputs and outputs –ALU (Arithmetic and Logic Unit) -- operations on data Sequential Logic –State machine -- coordinate control signals and data movement Temporary (scratchpad) Memory –Registers and latches -- storage elements

LC-3 Data Path: Combinational Logic State Machine Storage

Data Path of the LC-3

Computer Machine Instruction Formats What is IN an instruction? Specifies the operation to be performed Where to get the operands Where to put the result What are the major instruction types? Data Movement (load, store, etc.) Operate (add, sub, mult,OR, AND, etc.) Control (branch, jump to subroutine, etc.)

The Machine Instruction Necessary information: Operation code Input Operand(s) Output Operand(s) Typical Operation formats: 1 operand 2 operands 3 operands Alternative Instruction Design Strategies Cisc (Complex Instruction Set Architecture) Risc (Reduced Instruction Set Architecture)

The LC-3 Instruction FORMAT – generally 2 operand Operation code Input Operand(s) Output Operand(s) Where are the operands? Memory Registers