| 8086 Microprocessor |
INTRODUCTION
The 8086 is Intels first 16 bit MP.It is designed using the HMOS technology and contains approximately 29,000 transistors.
The 8086 is packaged in a 40 pin DIP(Dual in line package) and requires a single 5V power supply.The standard 8086 runs at 5 MHz internal clock frequency,whereas the 8086-2 and 8086-4 run at internal clock frequencies of 8 and 4 MHz respectively.
An Intel 8254 external clock generator/driver chip is needed to generate the 8086 clock input signal.The 8086 divides the external clock connected at the CLK pin internally by three.Therefore for 5 MHz internal clock,the 8284 must generate 15 MHz at its output,which will be given to the CLK pin of 8086.
The 8086 has a 20 bit address,therefore
it can directly address upto 2*20=1 M byte of memory.The 8086 uses a segmented memory.
The 8086 family consists of two types of 16
bit microprocessors-the 8086 and 8088.The 8088 has an 8 bit external data path to memory
and I/O,while 8086 has a 16 bit external data path.The 8088 accesses memory in
bytes.A 8086 can be configured as a small uniprocessor system(Minimum mode,MN/~MX=HIGH) or
as a Multiprocessor system(Maximum mode,MN/~MX=LOW).
As shown above the 8086 is internally divided into two separate functional units.These are the Bus Interface Unit (BIU) and the Execution Unit (EU).This concept of dividing work between two processors and processing it simultaneously speeds up the execution.This is called Parallel processing.
BUS INTERFACE UNIT
The BIU sends out address,fetches instruction from memory,reads data from ports and memory and writes data to ports and memory.In other words the BIU handles all transfers of data and addresses on the buses for the execution unit.
INSTRUCTION QUEUE
To speed up the program execution BIU fetches as many as 6 instruction bytes ahead of tome from memory.The pre fetch instruction bytes are held for the EU in FIFO group of registers called Instruction Queue.The BIU can be fetching instruction bytes while EU is decoding or executing an instruction,which does not require the use of buses.
When the EU is ready for its next instruction it simply reads the instruction from the queue in the BIU.This pre fetch and Queue scheme greatly speeds up processing.Fetching the next instruction while the current instruction executes is called Pipelining.
EXECUTION UNIT
The EU of the 8086 tells the BIU,where to fetch instructions or data from,decodes instruction and executes instructions.The EU contains a 16 bit ALU which can add, subtract, AND, OR, XOR, increment, decrement, compliment or shift binary numbers.
Computer Organization - Introduction
8086 Assembly Language Programs
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