Lecture #30 Page 1 ECE 4110– Sequential Logic Design Lecture #30 Agenda 1.von Neumann Stored Program Computer Architecture Announcements 1.N/A.

Lecture #30 Page 2 von Neumann Computer von Neumann Stored Program Computer - "Stored Program" means the HW is designed to execute a set of pre-defined instructions - the program and data reside in a storage unit (i.e., memory) - to change the functionality of the computer, the program is changed (instead of the HW) - John von Neumann was a mathematician who described a computer architecture where the instructions and data reside in the same memory - this implies sequential execution - it is simple from the standpoint of state machine timing - the drawback is the "von Neumann bottleneck" in getting data into and out of memory in order for the computer to run - this architecture is what we are using in the labs on the Freescale microcontrollers –(in ECE 3120, ECE4140)

Lecture #30 Page 3 von Neumann Computer Block Diagram of von Neumann Computer

Lecture #30 Page 4 von Neumann Computer Block Diagram of the Central Processing Unit (CPU)

Lecture #30 Page 5 von Neumann Computer Central Processing Unit (CPU) - the CPU consists of: 1) Control Unit - the state machine that directs the execution of instructions. - for a given Opcode, the state machine traverses a specific path within its state diagram - also called the "Sequence Controller" or "Sequencer" 2) Processing Unit- contains all of the registers and ALU that hold and manipulate data - memory signals (data/address) coming into/out-of this unit 3) Control Signals- signals sent to processing unit from the control unit - direct data flow - load data into registers - select ALU operation - manage memory access signals 4) Test Signals- signals sent to control unit from the processing unit - results of operations that effect state machine flow

Lecture #30 Page 6 von Neumann Computer Processing Unit - let's start with the registers within the processing unit Instruction Registers (IR) - holds the Opcode that is read from memory - passes the Opcode to the Control Unit as a test signal Memory Address Reg (MAR) - holds the current address being sent to memory Program Counter (PC) - tracks the address of which instruction is being executed - PC is sequential (0,1,2…) - PC is loaded during a branch, incremented otherwise - MAR tracks PC when executing instruction User-Controlled Reg (X, Y,..)- these are operated on directly by the program - can be loaded and stored ALU Operand Register (Z)- holds one of the inputs to the ALU - the other input comes from one of the user-controlled registers

Lecture #30 Page 7 von Neumann Computer Processing Unit Arithmetic / Logic Unit (ALU) - performs data math and manipulation - we first load Z with the first input - we then select which user-controlled register is the other input - the control unit sends select lines to indicate which operation to perform Condition Code Register (CCR) - tracks the status of ALU operations (i.e., NZVC) - these signals are sent to the control unit in order to alter sequence flow

Lecture #30 Page 8 von Neumann Computer Buses - we route data in the processing unit between registers/memory using shared lines called buses - for this architecture, we need two buses Bus1- can take either PC or the User-Controlled Registers - will drive to Memory_In or Bus 2 Bus2- can take either ALU, Bus1, or Memory_Out - will drive to IR, MAR, PC, User-Controlled Registers, or ALU Operand Reg - Information from Bus1 can be routed to Bus2 for feedback operations (PC = PC + 1) - Bus select lines come from the Control Unit to select which information is on which bus at any given time.