Advanced Microprocessor & Interfacing

Intel 8086 Intel 8086 microprocessor is the enhanced version of Intel 8085 microprocessor. It was designed by Intel in 1976. The 8086 microprocessor is a16-bit, N-channel, HMOS microprocessor. Where the HMOS is used for " High-speed Metal Oxide Semiconductor ". Intel 8086 is built on a single semiconductor chip and packaged in a 40-pin IC package. The type of package is DIP (Dual Inline Package). Intel 8086 uses 20 address lines and 16 data- lines. It can directly address up to 2 20  = 1 Mbyte of memory. It consists of a powerful instruction set, which provides operation like division and multiplication very quickly. 8086 is designed to operate in two modes, i.e., Minimum and Maximum mode. Difference between 8085 and 8086 Microprocessor 8085 Microprocessor 8086 Microprocessor It is an 8-bit microprocessor. It is a 16-bit microprocessor. It has a 16-bit address line. It has a 20-bit address line. It has a 8-bit data bus. It has a 16-bit data bus. The memory capacity is 64 KB. ...

8086 pins configuration The description of the pins of 8086 is as follows: AD0-AD15 (Address Data Bus):  Bidirectional address/data lines. These are low order address bus. They are multiplexed with data. When these lines are used to transmit memory address, the symbol A is used instead of AD, for example, A0- A15. A16 - A19 (Output):  High order address lines. These are multiplexed with status signals. A16/S3, A17/S4:  A16 and A17 are multiplexed with segment identifier signals S3 and S4. A18/S5:  A18 is multiplexed with interrupt status S5. A19/S6:  A19 is multiplexed with status signal S6. BHE /S7 (Output):  Bus High Enable/Status. During T1, it is low. It enables the data onto the most significant half of data bus, D8-D15. 8-bit device connected to upper half of the data bus use BHE signal. It is multiplexed with status signal S7. S7 signal is available during T3 and T4. RD  (Read):  For read operation. It is an output signal. It is active when...

8086 contains two independent functional units:  a Bus Interface Unit (BIU)  and an  Execution Unit (EU) . Fig: Block Diagram of Intel 8086 Microprocessor (8086 Architecture) Bus Interface Unit (BIU) The segment registers, instruction pointer and 6-byte instruction queue are associated with the bus interface unit (BIU). The BIU: Handles transfer of data and addresses, Fetches instruction codes, stores fetched instruction codes in first-in-first-out register set called a  queue , Reads data from memory and I/O devices, Writes data to memory and I/O devices, It relocates addresses of operands since it gets un-relocated operand addresses from EU. The EU tells the BIU from where to fetch instructions or where to read data. It has the following functional parts: Instruction Queue:  When EU executes instructions, the BIU gets 6-bytes of the next instruction and stores them in the instruction queue and this process is known as instruction pre fetch. This process increa...

An interrupt   is a process of creating a temporary halt during program execution and allows peripheral devices to access the microprocessor. The microprocessor responds to these interrupts with an  interrupt service routine (ISR) , which is a short program or subroutine to instruct the microprocessor on how to handle the interrupt. There are different types of interrupt in 8086: Hardware Interrupts Hardware interrupts  are that type of interrupt which are caused by any peripheral device by sending a signal through a specified pin to the microprocessor. The Intel 8086 has two hardware interrupt pins: NMI (Non-Maskbale Interrupt) INTR (Interrupt Request) Maskable Interrupt. NMI:  NMI is a single Non-Maskable Interrupt having higher priority than the maskable interrupt. It cannot be disabled (masked) by user using software. It is used by the processor to handle emergency conditions. For example:  It can be used to save program and data in case of power failure. An...

  The way for which an operand is specified for an instruction in the accumulator, in a general purpose register or in memory location, is called   addressing mode . The 8086 microprocessors have 8 addressing modes. Two addressing modes have been provided for instructions which operate on register or immediate data. These two addressing modes are: Register Addressing:  In register addressing, the operand is placed in one of the 16-bit or 8-bit general purpose registers. Example MOV AX, CX ADD AL, BL ADD CX, DX Immediate Addressing:  In immediate addressing, the operand is specified in the instruction itself. Example MOV AL, 35H MOV BX, 0301H MOV [0401], 3598H ADD AX, 4836H The remaining 6 addressing modes specify the location of an operand which is placed in a memory. These 6 addressing modes are: Direct Addressing:  In direct addressing mode, the operand?s offset is given in the instruction as an 8-bit or 16-bit displacement element. Example ADD AL, [0301] The ...

A   Microprocessor   is an Integrated Circuit with all the functions of a CPU. However, it cannot be used stand-alone since unlike a microcontroller it   has no memory or peripherals .  8086 does not have RAM or ROM inside it. However, it has  internal registers  for storing intermediate and final results and interfaces with memory located outside it through the System Bus.  In the case of 8086, it is a 16-bit  Integer processor  in a 40-pin, Dual Inline Packaged IC.  The size of the internal registers(present within the chip) indicates how much information the processor can operate on at a time ( in this case 16-bit registers ) and how it moves data around internally within the chip, sometimes also referred to as the internal data bus.  8086 provides the programmer with 14 internal registers, each of 16 bits or 2 bytes wide.  The main advantage of the 8086 microprocessor is that it supports Pipelining. 8086 Architecture M...