Features Of 8086 Microprocessor

[Antonio Brittenham]

The8086 microprocessor is an 8-bit/16-bit microprocessor designed by Intel in the late 1970s. It is the first member of the x86 family of microprocessors, which includes many popular CPUs used in personal computers.

The architecture of the 8086 microprocessor is based on a complex instruction set computer (CISC) architecture, which means that it supports a wide range of instructions, many of which can perform multiple operations in a single instruction. The 8086 microprocessor has a 20-bit address bus, which can address up to 1 MB of memory, and a 16-bit data bus, which can transfer data between the microprocessor and memory or I/O devices.

The 8086 microprocessor has a segmented memory architecture, which means that memory is divided into segments that are addressed using both a segment register and an offset. The segment register points to the start of a segment, while the offset specifies the location of a specific byte within the segment. This allows the 8086 microprocessor to access large amounts of memory, while still using a 16-bit data bus.

The 8086 microprocessor has two main execution units: the execution unit (EU) and the bus interface unit (BIU). The BIU is responsible for fetching instructions from memory and decoding them, while the EU executes the instructions. The BIU also manages data transfer between the microprocessor and memory or I/O devices.

The 8086 microprocessor has a rich set of registers, including general-purpose registers, segment registers, and special registers. The general-purpose registers can be used to store data and perform arithmetic and logical operations, while the segment registers are used to address memory segments. The special registers include the flags register, which stores status information about the result of the previous operation, and the instruction pointer (IP), which points to the next instruction to be executed.

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.

The Prefetch Unit in the 8086 microprocessor is a component responsible for fetching instructions from memory and storing them in a queue. The prefetch unit allows the 8086 to perform multiple instruction fetches in parallel, improving the overall performance of the microprocessor.

The prefetch unit consists of a buffer and a program counter that are used to fetch instructions from memory. The buffer stores the instructions that have been fetched and the program counter keeps track of the memory location of the next instruction to be fetched. The prefetch unit fetches several instructions ahead of the current instruction, allowing the 8086 to execute instructions from the buffer rather than from memory.

This parallel processing of instruction fetches helps to reduce the wait time for memory access, as the 8086 can continue to execute instructions from the buffer while it waits for memory access to complete. This results in improved overall performance, as the 8086 is able to execute more instructions in a given amount of time.

The prefetch unit is an important component of the 8086 microprocessor, as it allows the microprocessor to work more efficiently and perform more instructions in a given amount of time. This improved performance helps to ensure that the 8086 remains competitive in its performance and capabilities, even as technology continues to advance.

The Decode Unit works in parallel with the Prefetch Unit, which fetches instructions from memory and stores them in a queue. The Decode Unit reads the instructions from the queue and translates them into micro-operations that can be executed by the microprocessor.

The Decode Unit is an important component of the 8086 microprocessor, as it allows the microprocessor to execute instructions efficiently and accurately. The decode unit ensures that the microprocessor can execute complex instructions, such as jump instructions and loop instructions, by translating them into a series of simple micro-operations.

The Decode Unit is responsible for decoding instructions, performing register-to-register operations, and performing memory-to-register operations. It also decodes conditional jumps, calls, and returns, and performs data transfers between memory and registers.

The Decode Unit helps to improve the performance of the 8086 microprocessor by allowing it to execute instructions quickly and accurately. This improved performance helps to ensure that the 8086 remains competitive in its performance and capabilities, even as technology continues to advance.

The Control Unit in the 8086 microprocessor is a component that manages the overall operation of the microprocessor. The control unit is responsible for controlling the flow of instructions through the microprocessor and coordinating the activities of the other components, including the Decode Unit, Execution Unit, and Prefetch Unit.

The Control Unit acts as the central coordinator for the microprocessor, directing the flow of data and instructions and ensuring that the microprocessor operates correctly. It also monitors the state of the microprocessor, ensuring that the correct sequence of operations is followed.

The Control Unit is an essential component of the 8086 microprocessor, as it allows the microprocessor to operate efficiently and accurately. The control unit ensures that the microprocessor can execute complex instructions, such as jump instructions and loop instructions, by coordinating the activities of the other components.

The Control Unit helps to improve the performance of the 8086 microprocessor by managing the flow of instructions and data through the microprocessor, ensuring that the microprocessor operates correctly and efficiently. This improved performance helps to ensure that the 8086 remains competitive in its performance and capabilities, even as technology continues to advance.

1.Address Bus: The address bus is used to send the memory address of the instruction or data being read or written. The address bus is 16 bits wide, allowing the 8086 to address up to 64 kilobytes of memory.

3.Control Bus: The control bus is used to transfer control signals between the microprocessor and other components in the computer system. The control bus is used to send signals such as read, write, and interrupt requests, and to transfer status information between the microprocessor and other components.

sometime ago I built an emulator for the 8086 chip and now I'm wanting to actually own one and set one up for some bit banging and such. Note, I'm not interested in all the PC specifics(DMA, PIC, BIOS, etc) only the bare basics to get the 8086 to run some code, which as I understand only requires a power supply, oscillator/clock source, and some RAM(unknown which type?)

So, for the most part all of the components are easy to find except for the one I need: The 8086 processor itself. I've not been able to find anything but (very pricey) collector's items 8086 chips. So where can I find a reasonably priced replica 8086 chip? Note: The pin out doesn't need to be the exact same, but I'd prefer it to be DIP and expose all of the features of the 8086. Also, don't just say "try buying an old 486 computer" After the 8086, the x86 line of processors got insanely complex. For this reason, I'm sticking to just the 8086. Though possibly an 8186 would be OK.

The Intel 8086 microprocessor was introduced 42 years ago this month,1 so I made some high-res die photos of the chip to celebrate.The 8086 is one of the most influential chips ever created; it started the x86 architecture that stilldominates desktop and server computing today.By looking at the chip's silicon, we can see the internal features of this chip.

The photo below shows the die of the 8086. In this photo, the chip's metal layer is visible,mostly obscuring the silicon underneath.Around the edges of the die, thin bond wires provide connections between pads on the chip and the external pins.(The power and ground pads each have two bond wires to support the higher current.)The chip was complex for its time, containing 29,000 transistors.

To examine the die, I started with the 8086 integrated circuit below.Most integrated circuits are packaged in epoxy, so dangerous acids are necessary to dissolve the package.To avoid that, I obtained the 8086 in a ceramic package instead.Opening a ceramic package is a simple matter of tapping it along the seam with a chisel, popping the ceramic top off.

With the top removed, the silicon die is visible in the center.The die is connected to the chip's metal pins via tiny bond wires.This is a 40-pin DIP package, the standard packaging for microprocessors at the time.Note that the silicon die itself occupies a small fraction of the chip's size.

Using a metallurgical microscope, I took dozens of photos of the die and stitched them into a high-resolution imageusing a program called Hugin (details).The photo at the beginning of the blog post shows the metal layer of the chip, but this layer hid the siliconunderneath.

For the die photo below, the metal and polysilicon layers were removed, showing the underlying silicon with its29,000 transistors.2The labels show the main functional blocks, based on my reverse engineering.The left side of the chip contains the 16-bit datapath: the chip's registers and arithmetic circuitry.The adder and upper registers form the Bus Interface Unit that communicates with external memory,while the lower registers and the ALU form the Execution Unit that processes data.The right side of the chip has control circuitry and instruction decoding, along with themicrocode ROM that controls each instruction.

One feature of the 8086 was instruction prefetching, which improved performance by fetching instructions from memorybefore they were needed.This was implemented by the Bus Interface Unit in the upper left, which accessed external memory.The upper registers include the 8086's infamous segment registers, which provided access to a larger address space thanthe 64 kilobytes allowed by a 16-bit address. For each memory access, a segment register and a memory offset wereadded to form the final memory address.For performance, the 8086 had a separate adder for these memory address computations, rather than using the ALU.The upper registers also include six bytes of instruction prefetch buffer and the program counter.

3a8082e126