technology 8086

The 8086 is a true 16bit machine which means that the ALU (Arithmetic Logic Unit) is designed to work with 16bit numbers and the data bus is also 16bits wide, because the 8088 is hybrid in that the ALU is 16bits but the data bus is 8bits. In almost every other respect the two processors are identical. It is possible to address 1Mbyte of memory with the 20bit address bus. Both devices have time multiplexed address and data buses and some of the control pins have more than one function depending upon whether the device is operated in the min or max mode. The min mode is designed for small single processor systems whilst in the max mode the device is designed to work in medium or large systems using more than one processor.

Incidentally, the 8086 is some 7x to 10x more powerful than the 8080. To speed up execution time, instructions are pre-fetched or pipelined into the microprocessor thereby almost eliminating instruction fetch time. This has been achieved by incorporating two separate processing units inside the 8086. The bus Interface Unit (BIU) and the Execution Unit (EU). Basically the BIU fetches instructions and the EU executes them.

One of the problems with moving to a new processor is, having to learn a completely new set of instructions so that effective assembly language code can be written. Intel has designed its processors so that they are upwardly compatible. Code written for say, an 8085 system will also run on an 8086 system. What you can't guarantee is the reverse since the 8086 has instructions that the 8085 doesn't. But if time is tight, then upgrading to the 8086 does not pose much of a problem or those familiar with the 8080/808

The 8085 is a conventional von Neumann design based on the Intel 8080. Unlike the 8080 it had no state signals multiplexed onto the data bus, but the 8-bit data bus was instead multiplexed with the lower part of the 16-bit address bus to limit the number of pins to 40. The processor was designed using nMOS circuitry and the later "H" versions were implemented in Intel's enhanced nMOS process called HMOS, originally developed for fast static RAM products. Only a 5 Volt supply was needed, like competing processors and unlike the 8080. The 8085 used approximately 6,500 transistors.^[1]

The 8085 incorporated the functionality of the 8224 (clock generator) and the 8228 (system controller), increasing the level of integration. A downside compared to similar contemporary designs (such as the Z80) was the fact that the buses required demultiplexing; however, address latches in the Intel 8155, 8355, and 8755 memory chips allowed a direct interface, so an 8085 along with these chips was almost a complete system.

The 8085 had extensions to support new interrupts: It had three maskable interrupts (RST 7.5, RST 6.5 and RST 5.5), one non-maskable interrupt (TRAP), and one externally serviced interrupt (INTR). The RST n.5 interrupts refer to actual pins on the processor, a feature which permitted simple systems to avoid the cost of a separate interrupt controller.

Like the 8080, the 8085 could accommodate slower memories through externally generated wait states (pin 35, READY), and had provisions for Direct Memory Access (DMA) using HOLD and HLDA signals (pins 39 and 38). An improvement over the 8080 was that the 8085 can itself drive a piezoelectric crystal directly connected to it, and a built in clock generator generates the internal high amplitude two-phase clock signals at half the crystal frequency (a 6.14 MHz crystal would yield a 3.07 MHz clock, for instance).

5/Z80 microprocessors.

MICROPROCESSOR 8085

The 8085 is a conventional von Neumann design based on the Intel 8080. Unlike the 8080 it had no state signals multiplexed onto the data bus, but the 8-bit data bus was instead multiplexed with the lower part of the 16-bit address bus to limit the number of pins to 40. The processor was designed using nMOS circuitry and the later "H" versions were implemented in Intel's enhanced nMOS process called HMOS, originally developed for fast static RAM products. Only a 5 Volt supply was needed, like competing processors and unlike the 8080. The 8085 used approximately 6,500 transistors.^[1]