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The true distinction of a Harvard machine is that instruction and data memory occupy different address spaces. In other words, a memory address does not uniquely identify a storage location (as it does in a von Neumann machine); it is also necessary to know the memory space (instruction or data) to which the address belongs.
Harvard architecture. The Harvard architecture is a computer architecture with separate storage [1] and signal pathways for instructions and data.It is often contrasted with the von Neumann architecture, where program instructions and data share the same memory and pathways.
Note that this is more or less the same as base-plus-offset addressing mode, except that the offset in this case is large enough to address any memory location. Example 1: Within a subroutine, a programmer may define a string as a local constant or a static variable. The address of the string is stored in the literal address in the instruction.
CISC — Often machines are limited to one memory operand per instruction: load a,reg1; add b,reg1; store reg1,c; This requires a load/store pair for any memory movement regardless of whether the add result is an augmentation stored to a different place, as in C = A+B, or the same memory location: A = A+B. C = A+B needs three instructions. RISC ...
The number of operands is one of the factors that may give an indication about the performance of the instruction set. A three-operand architecture (2-in, 1-out) will allow A := B + C to be computed in one instruction ADD B, C, A A two-operand architecture (1-in, 1-in-and-out) will allow A := A + B to be computed in one instruction ADD B, A
The AVR is a modified Harvard architecture machine, where program and data are stored in separate physical memory systems that appear in different address spaces, but having the ability to read data items from program memory using special instructions.
Note that the instruction sequence follows the pattern of A-instruction, C-instruction, A-instruction, C-instruction, ... . This is typical for Hack assembly language programs. The A-instruction specifies a constant or memory address that is used in the subsequent C-instruction. All three variations of the A-instruction are illustrated.
The fetch stage is the same for each instruction: The PC contains the address of the instruction to be fetched. This address is copied to the MAR, where this address is used to poll for the location of the instruction in memory. The CU sends a signal to the control bus to read the memory at the address in MAR - the data read is placed in the ...