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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.
Four registers are used to refer to four segments on the 16-bit x86 segmented memory architecture. DS (data segment), CS (code segment), SS (stack segment), and ES (extra segment). Another 16-bit register can act as an offset into a given segment, and so a logical address on this platform is written segment:offset, typically in hexadecimal ...
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.
Computer architectures are often described as n-bit architectures. In the first 3 ⁄ 4 of the 20th century, n is often 12, 18, 24, 30, 36, 48 or 60.In the last 1 ⁄ 3 of the 20th century, n is often 8, 16, or 32, and in the 21st century, n is often 16, 32 or 64, but other sizes have been used (including 6, 39, 128).
Such "two-address format" ISAs are very common. One can further extend the concept to a "three-address format" where the SAVE is also folded into an expanded ADD address 1, address 2, address of result. [4] It is often the case that the basic computer word is much larger than needed to hold just the instruction and an address, and in most ...
Two memory-destination forms of this operation, ANL address, #data and ANL address, A, are specified by opcodes 0x53 and 0x52. 6y: XRL A, operand Logical exclusive-OR the operand into the accumulator. Two memory-destination forms of this operation, XRL address, #data and XRL address, A, are specified by opcodes 0x63 and 0x62. 7y: MOV operand, #data
In other words, this register is used to access data and instructions from memory during the execution phase of instruction. MAR holds the memory location of data that needs to be accessed. When reading from memory, data addressed by MAR is fed into the MDR (memory data register) and then used by the CPU. When writing to memory, the CPU writes ...
Models with >256 bytes of data address space (≥256 bytes of RAM) have a 16-bit stack pointer, with the high half in the SPH register. Models with >8 KiB of ROM add the 2-word (22-bit) JUMP and CALL instructions. (Some early models suffer an erratum if a skip instruction is followed by a 2-word instruction.)