8086mp

rchitecture of 8086 Unlike microcontrollers, microprocessors do not have inbuilt memory. Mostly Princeton architecture is used for microprocessors where data and program memory are combined in a single memory interface. Since a microprocessor does not have any inbuilt peripheral, the circuit is purely digital and the clock speed can be anywhere from a few MHZ to a few hundred MHZ or even GHZ. This increased clock speed facilitates intensive computation that a microprocessor is supposed to do. We will discuss the basic architecture of Intel 8086 before discussing more advanced microprocessor architectures. Internal architecture of Intel 8086: Intel 8086 is a 16 bit integer processor. It has 16-bit data bus and 20-bit address bus. The lower 16-bit address lines and 16-bit data lines are multiplexed (AD0-AD15). Since 20-bit address lines are available, 8086 can access up to 2 20 or 1 Giga byte of physical memory. The basic architecture of 8086 is shown below. Fig 29.1  Basic Architecture of 8086 Microprocessor The internal architecture of Intel 8086 is divided into two units, viz., Bus Interface Unit (BIU) and Execution Unit (EU). Bus Interface Unit (BIU ) The Bus Interface Unit (BIU) generates the 20-bit physical memory address and provides the interface with external memory (ROM/RAM). As mentioned earlier, 8086 has a single memory interface. To speed up the execution, 6-bytes of instruction are fetched in advance and kept in a 6-byte Instruction Queue while other instructions are being executed in the Execution Unit (EU). Hence after the execution of an instruction, the next instruction is directly fetched from the instruction queue without having to wait for the external memory to send the instruction. This is called pipe-lining and is helpful for speeding up the overall execution process. 8086's BIU produces the 20-bit physical memory address by combining a 16-bit segment address with a 16-bit offset address. There are four 16-bit segment registers, viz., the code segment (CS), the stack segment (SS), the extra segment (ES), and the data segment (DS). These segment registers hold the corresponding 16-bit segment addresses. A segment address is the upper 16-bits of the starting address of that segment. The lower 4-bits of the starting address of a segment is always zero. The offset address is held by another 16-bit register. The physical 20-bit address is calculated by shifting the segment address 4-bit left and then adding that to the offset address. For Example: Code segment Register CS holds the segment address which is 4569 H Instruction pointer IP holds the offset address which is 10A0 H The physical 20-bit address is calculated as follows. Segment address :  45690 H Offset address       :+  10A0 H Physical address  :  46730 H

MICRO PROCESSORS

What is a Microcontroller?

A Microcontroller is a programmable digital processor with necessary peripherals. Both microcontrollers and microprocessors are complex sequential digital circuits meant to carry out job according to the program / instructions. Sometimes analog input/output interface makes a part of microcontroller circuit of mixed mode(both analog and digital nature). A microcontroller can be compared to a Swiss knife with multiple functions incorporated in the same IC.

Fig. 1.1     A Microcontroller compared with a Swiss knife

Microcontrollers Vs Microprocessors

A microprocessor requires an external memory for program/data storage. Instruction execution requires movement of data from the external memory to the microprocessor or vice versa. Usually, microprocessors have good computing power and they have higher clock speed to facilitate faster computation. A microcontroller has required on-chip memory with associated peripherals. A microcontroller can be thought of a microprocessor with inbuilt peripherals. A microcontroller does not require much additional interfacing ICs for operation and it functions as a stand alone system. The operation of a microcontroller is multipurpose, just like a Swiss knife. Microcontrollers are also called embedded controllers. A microcontroller clock speed is limited only to a few tens of MHz. Microcontrollers are numerous and many of them are application specific.

Development/Classification of microcontrollers (Invisible)

Microcontrollers have gone through a silent evolution (invisible). The evolution can be rightly termed as silent as the impact or application of a microcontroller is not well known to a common user, although microcontroller technology has undergone significant change since early 1970's. Development of some popular microcontrollers is given as follows.

Intel 4004 4 bit (2300 PMOS trans, 108 kHz) 1971 Intel 8048 8 bit 1976 Intel 8031 8 bit (ROM-less) . Intel 8051 8 bit (Mask ROM) 1980 Microchip PIC16C64 8 bit 1985 Motorola 68HC11 8 bit (on chip ADC) . Intel 80C196 16 bit 1982 Atmel AT89C51 8 bit (Flash memory) . Microchip PIC 16F877 8 bit (Flash memory + ADC) .

Development of microprocessors (Visible)

Microprocessors have undergone significant evolution over the past four decades. This development is clearly perceptible to a common user, especially, in terms of phenomenal growth in capabilities of personal computers. Development of some of the microprocessors can be given as follows.

Intel 4004 4 bit (2300 PMOS transistors) 1971 Intel 8080          8085 8 bit (NMOS) 8 bit 1974 Intel 8088          8086 16 bit 16 bit 1978 Intel 80186          80286 16 bit 16 bit 1982 Intel 80386 32 bit (275000 transistors) 1985 Intel 80486 SX                      DX 32 bit 32 bit (built in floating point unit) 1989 Intel 80586     I                          MMX                          Celeron II                          III                          IV 64 bit 1993 1997 1999 2000 Z-80 (Zilog) 8 bit 1976 Motorola Power PC     601                                         602                                         603 32-bit 1993 1995