1 بسم الله الرحمن الرحيم MEMORY AND I/O

Introduction to 8086 Microprocessor 8086 Pin Configuration Pin Configuration 8086 Architecture & Modes 2

 Memory Organization  Memory Interface Techniques  Memory Array Design  Microprocessor Input/ Output  Memory array Design Examples 3

4  A memory unit is an integral part of any microcomputer system, and its primary purpose is to hold instructions and data  The major design goal of a memory unit is to allow it to operate at a speed close to that of the processor

5  In order to seek a trade-off between the cost and operating speed, a memory system is usually designed with different technologies such as solid state, magnetic, and optical  A microcomputer memory: Processor Memory - Primary [ Main ] Memory - Secondary Memory

6  Processor memory refers to a set of microprocessor registers  These registers are used to hold temporary results when a computation is in progress  The cost involved in this approach limits a microcomputer architect to include only a few registers in the microprocessor

7  Main memory is the storage area in which all programs are executed. The microprocessor can directly access only those items that are stored in main memory  All programs must be within the main memory prior to execution

8  The size of the main memory is usually much larger than processor memory and its operating speed is slower than the processor registers  Main memory normally includes ROMs and RAMs

9  Electromechanical memory devices such as disks are extensively used as microcomputer’s secondary memory and allow storage of large programs at a low cost  These secondary memory devices access stored data serially

10  They are significantly slower than the main memory. Popular secondary memories include hard disk and floppy disk systems  Programs are stored on the disks in files  Secondary memory stores programs in excess of the main memory

11  Secondary memory is also referred to as “auxiliary” or “virtual” memory  The microcomputer cannot directly execute programs stored in the secondary memory, so in order to execute these programs; the microcomputer must transfer them to its main memory by a program called the “operating system”

12  In a typical microcomputer application, a designer has to implement the required capacity by interconnecting several small memory chips  This concept is known as the “memory array design”

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16  To connect a microprocessor to ROM/RAM chips, three address-decoding techniques are usually used:  Linear decoding  Full decoding  Memory decoding using PLDs

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19  This method is known as “linear select decoding”  Its primary advantage is that it does not require any decoding hardware  If two or or more lines of A10 through A13 are low at the same time, more than one RAM chip are selected, [a bus conflict]

20  Because of this potential problem, the software must be written in such a way that it never reads into or writes from any address in which more than one of the bits A13 through A10 are low  Another disadvantage of this method is that it wastes a large amount of address space

21  For example, whenever the address value is B800H or 3800H, the RAM chip I is selected  In other words, the address 3800H is the mirror reflection of the address B800H  This situation is also called “memory foldback”  This technique is limited to a small system

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23  This approach does not waste any address space. The address map is shown below: