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An address decoder is a particular use of a binary decoder circuit known as a "demultiplexer" or "demux" (the 74154 is commonly called a "4-to-16 demultiplexer"), which has many other uses besides address decoding. Address decoders are fundamental building blocks for systems that use buses.
The Intel 8085 ("eighty-eighty-five") is an 8-bit microprocessor produced by Intel and introduced in March 1976. [2] It is the last 8-bit microprocessor developed by Intel. It is software-binary compatible with the more-famous Intel 8080 with only two minor instructions added to support its added interrupt and serial input/output features.
This process is much faster than sending out an address, reading the opcode and then decoding and executing it. Fetching the next instruction while the current instruction is being decoded or executed is called pipelining. [8] The 8086 processor has a six-byte prefetch instruction pipeline, while the 8088 has a four-byte prefetch. As the ...
Such address translations are carried out by the segmentation unit of the CPU. The last segment, FFFFh (65535), begins at linear address FFFF0h (1048560), 16 bytes before the end of the 20 bit address space, and thus, can access, with an offset of up to 65,536 bytes, up to 65,520 (65536−16) bytes past the end of the 20 bit 8088 address space.
The 8086 [3] (also called iAPX 86) [4] is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, [5] is a slightly modified chip with an external 8-bit data bus (allowing the use of cheaper and fewer supporting ICs), [note 1] and is notable as the processor used in the original IBM PC design.
Intel designed the 8086 to have its assembly language be similar enough to the 8080, with most instructions mapping directly onto each other, that transpiled 8080 assembly code could be executed on the 8086. [7] The initial specified clock rate or frequency limit was 2 MHz, with common instructions using 4, 5, 7, 10, or 11 clock cycles.
The priority interrupt system was queried before decoding of every address word. [26] So, an indirect address loop would not prevent execution of device service routines, including any preemptive multitasking scheduler's time-slice expiration handler. A looping instruction would be treated like any other compute-bound job.
The Intel 8086, Intel 8088, and Intel 80186 processors had 20 address lines, numbered A0 to A19; with these, the processor can access 2 20 bytes, or 1 MB. Internal address registers of such processors only had 16 bits.