8086 is a
16bit processor. It’s ALU, internal registers works with 16bit binary word .
8086 has a
16bit data bus. It can read or write data to a memory/port either 16bits or 8
bit at a time
8086 has a
20bit address bus which means, it can address upto 220 = 1MB memory
location
Frequency range of
8086 is 6-10 MHz
The microprocessors functions as the
CPU in the stored program model of the digital computer. Its job is to generate
all system timing signals and synchronize the transfer of data between memory,
I/O, and itself. The microprocessor also has a S/W function. It must
recognize, decode, and execute program instructions fetched from the memory
unit. This requires an Arithmetic-Logic Unit (ALU) within the CPU to perform
arithmetic and logical (AND, OR, NOT, compare, etc) functions.
The 8086 CPU is organized as two
separate units, called the Bus Interface
Unit (BIU) and the Execution Unit
(EU). The BIU provides H/W functions, including generation of the memory
and I/O addresses for the transfer of data between the outside world -outside
the CPU, and the EU.
The EU receives program instruction
codes and data from the BIU, executes these instructions, and store the results
in the general registers. By passing the data back to the BIU, data can also be
stored in a memory location or written to an output device. It receives and
outputs all its data thru the BIU.
Although the 8086 still functions as a stored program
computer, organization of the CPU into a separate BIU and EU allows the fetch
and execute cycles to overlap. To see this, consider what happens when the 8086
is first started.
1.
The
BIU outputs the contents of the instruction pointer register (IP) onto the
address bus, causing the selected byte or word to be read into the BIU.
2.
Register IP is incremented by 1 to prepare for
the next instruction fetch.
3.
Once
inside the BIU, the instruction is passed to the queue. This is a first-in,
first-out storage register sometimes likened to a "pipeline".
4. Assuming
that the queue is initially empty, the EU immediately draws this instruction
from the queue and begins execution.
5. While the EU is executing this instruction, the BIU
proceeds to fetch a new instruction. Depending on the execution time of the
first instruction, the BIU may fill the queue with several new instructions
before the EU is ready to draw its next instruction.
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