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Encyclopedia > Intel 8085
Intel 8085
Central processing unit

An Intel 8085AH processor.
Produced: mid 1970s
Manufacturer: Intel
CPU speeds: 3.07 Mhz to 5 Mhz
Instruction set: pre x86
Cores: 1
Socket: 40 pin DIP

The Intel 8085 was an 8-bit microprocessor made by Intel in the mid-1970s. It was binary compatible with the more-famous Intel 8080 but required less supporting hardware, thus allowing simpler and less expensive microcomputer systems to be built. “CPU” redirects here. ... Image File history File links Download high resolution version (2458x821, 405 KB) Summary Microprocessor Intel 8085 (P8085AH-2), 5 MHz, in 40-pin DIP (plastic) Photographed by de:User:Stefan506, on December 9, 2005 Licensing File links The following pages link to this file: Intel 8085 ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... “CPU” redirects here. ... This article is about the SI unit of frequency. ... This article is about the SI unit of frequency. ... It has been suggested that some sections of this article be split into a new article entitled instruction set architecture. ... x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... Diagram of an Intel Core 2 dual core processor, with CPU-local Level 1 caches, and a shared, on-die Level 2 cache. ... ICs in DIP14-Package Several PDIPs and CERDIPS. The large CERDIP in the foreground is an 8080 processor. ... 8-bit refers to the number of bits used in the data bus of a computer. ... A microprocessor is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... The 1970s decade refers to the years from 1970 to 1979, also called The Seventies. ... AMD clone NEC 8080AF (2nd-source). ...

The "5" in the model number came from the fact that the 8085 required only a +5-volt (V) power supply rather than the +5V, -5V and +12V supplies the 8080 needed. Both processors were sometimes used in computers running the CP/M operating system, and the 8085 later saw use as a microcontroller (much by virtue of its component count reducing feature). Both designs were eclipsed for desktop computers by the compatible but more capable Zilog Z80, which took over most of the CP/M computer market as well as taking a large share of the booming home computer market in the early-to-mid-1980s. The 8085 had a very long life as a controller. Once designed into such products as the DECtape controller and the VT100 video terminal in the late 1970s, it continued to serve for new production throughout the life span of those products (generally many times longer than the new manufacture lifespan of desktop computers). Josephson junction array chip developed by NIST as a standard volt. ... CP/M (Command Processor for Microcomputers) was an operating system for Intel 8080/85 and Zilog Z80 based microcomputers. ... It has been suggested that this article or section be merged with embedded microprocessor. ... One of the first Z80 microprocessors manufactured; the date stamp is from June 1976. ... Children playing on a Amstrad CPC 464 in the 1980s. ... DECtape was a magnetic tape storage medium used with early Digital Equipment Corporation computers, including the PDP-6, PDP-8, LINC-8, PDP-10, PDP-11, PDP-12, and the PDP-15. ... The VT100 was a video terminal made by Digital Equipment Corporation (DEC) which became the de facto standard used by terminal emulators. ...

However, it was somewhat slower than the 8080, and operated at 0.37 million instructions per second (MIPS) compared to 0.64 MIPS. [1] Million instructions per second (MIPS) is a measure of a computers processor speed. ...


CPU architecture

The 8085 Architecture follows the von Neumann architecture, with a 16bit address bus, and a 8bit data bus, but it is actually based on harvard concept.[citation needed] The 8085 incorporated all the features of the 8224 (clock generator) and the 8228 (system controller) increasing the level of system integration. The 8085 along with and 8156 RAM and 8355/8755 ROM/PROM constituted a complete system. The 8085 used a multiplexed Data Bus and required the 825X-5 support chips. The address was split between the 8-bit address bus and 8-bit data bus. The on-chip address latch of 8155/8355/8755 memory chips allowed a direct interface with the 8085. The initial 8085's were based on NMOS technology and the later "H" versions were based on HMOS technology. Design of the Von Neumann architecture For the robotic architecture also named after Von Neumann, see Von Neumann machine The von Neumann architecture is a computer design model that uses a single storage structure to hold both instructions and data. ...


The 8085 can access 216 (= 65,536) individual 8-bit memory locations, or in other words, its address space is 64 KB. Unlike some other microprocessors of its era, it has a separate address space for up to 28 (=256) I/O ports. It also has a built in register array which are usually labeled A(Accumulator), B, C, D, E, H, and L. Further special-purpose registers are the 16-bit Program Counter (PC), Stack Pointer (SP), and 8-bit flag register F. The microprocessor has 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 chip. A kilobyte (derived from the SI prefix kilo-, meaning 1,000) is a unit of information or computer storage equal to either 1,000 bytes or 1,024 bytes (210), depending on context. ... A Non-Maskable Interrupt (NMI) is a special type of interrupt that can not be ignored by standard interrupt masking techniques. ...


  • Address bus - 16 line bus accessing 216 memory locations (64 KB) of memory.
  • Data bus - 8 line bus accessing one 8-bit byte of data in one operation. Data bus width is the traditional measure of processor bit designations, as opposed to address bus width, resulting in the 8-bit microprocessor designation.
  • Control buses - Carries the essential signals for various operations.

Intel produced a series of development systems for the 8080 and 8085, known as the Personal Development System. The original PDS was a large box (in the Intel corporate blue colour) which included a CPU and monitor, and used 8 inch floppy disks. It ran the ISIS operating system and could also operate an emulator pod and EPROM programmer. The later iPDS was a much more portable unit featuring a small green screen and a 5¼ inch floppy disk drive, and ran the ISIS-II operating system. It could also accept a second 8085 processor, allowing a limited form of multi-processor operation where both CPUs shared the screen, keyboard and floppy disk drive. In addition to an 8080/8085 assembler, Intel produced a number of compilers including PL/M-80 and Pascal languages, and a set of tools for linking and statically locating programs to enable them to be burnt into EPROMs and used in embedded systems. This article is about the unit of information. ... In computer science a byte (pronounced bite) is a unit of measurement of information storage, most often consisting of eight bits. ... 8-bit refers to the number of bits used in the data bus of a computer. ... A microprocessor is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). ... This article is about emulators in computer science. ... EPROM. The small quartz window admits UV light during erasure. ... Intelligent Printer Data Stream (IPDS) describes the data stream used by a variety of IBM and OEM print servers that drive all-points-addressable (APA) page printers. ... CPU can stand for: in computing: Central processing unit in journalism: Commonwealth Press Union in law enforcement: Crime prevention unit in software: Critical patch update, a type of software patch distributed by Oracle Corporation in Macleans College is often known as Ash Lim. ... The PL/M programming language (an acronym of Programming Language for Microcomputers) is a medium-level language developed by MAA (later Digital Research) in 1972 on behalf of Intel for its microprocessors. ... Pascal is an imperative computer programming language, developed in 1970 by Niklaus Wirth as a language particularly suitable for structured programming. ... EPROM. The small quartz window admits UV light during erasure. ... A router, an example of an embedded system. ...

The 8085 as designed was upward-compatible in instruction set to the 8080, but had extensions to support new hardware (principally the RST n.5 interrupts) and to provide more efficient code. The hardware support changes were announced and supported, but the software upgrades were not supported by the assembler, user manual or any other means. At times it was claimed they were not tested when that was false.

The 8085 can accommodate slower memories through externally generated Wait states (pin 35, READY), and also has provisions for Direct Memory Access (DMA) using HOLD and HLDA signals (pins 39 and 38). A wait state is a delay experienced by a computer processor when accessing external memory or another device that is slow to respond. ... Direct memory access (DMA) is a feature of modern computers that allows certain hardware subsystems within the computer to access system memory for reading and/or writing independently of the central processing unit. ...

The 8085 runs on a timing crystal, connected to X1 and X2 (pins 1 and 2). There is divide by 2 counter in the 8085 causing it to actually run at 3.07MHz when connected to a 6.14 MHz crystal. A higher speed selection from the same production lots runs at 5 MHz.[2] A crystal oscillator is an electronic device that uses the mechanical resonance of a physical crystal of piezoelectric material to create an electrical signal with a very precise frequency. ...


For the extensive use of 8085 in various applications,the microprocessor is provided with an instruction set which consists of various instructions such as MOV, ADD, SUB, JMP etc.These instructions are written in the form of a program which is used to perform various operations such as addition, subtraction, multiplication( which is performed by repeated addition) and other arithmetic operations.

The 8085 processor has found marginal use in small scale computers up to the 21st century. The TRS-80 Model 100 line uses a 80C85. The CMOS version 80C85 of the NMOS/HMOS 8085 processor has/had several manufacturers, and some versions (eg. Tundra Semiconductor Corporation's CA80C85B) have additional functionality, eg. extra machine code instructions. One niche application for the rad-hard version of the 8085 has been in on-board instrument data processors for several NASA and ESA space physics missions in the 1990's and early 2000's, including CRRES, Polar, FAST, Cluster, HESSI, Sojourner (rover)[3], and THEMIS. The Swiss company SAIA used the 8085 and the 8085-2 as the CPUs of their PCA1 line of programmable logic controllers during the 1980s. TRS 80 Model 100 was a portable computer introduced in 1983, made by Kyocera, and sold by Radio Shack. ... For other uses, see CMOS (disambiguation). ... This article is about the American space agency. ... This article is about the European Space Agency. ... The Combined Release and Radiation Effects Satellite (CRRES) was launched on July 25, 1990 into a geosynchronous transfer orbit (GTO) for a nominal three-year mission to investigate fields, plasmas, and energetic particles inside the Earths magnetosphere. ... The Polar Satellite is a satellite launched by NASA on February 24, 1996 aboard a Boeing Delta II rocket from Vandenberg Air Force Base in California, to observe the polar magnetosphere. ... Reuven Ramaty High Energy Solar Spectroscopic Imager (or RHESSI) is a NASA sixth Small Explorer, launched on 5 February 2002. ... Sojourner next to the rock Barnacle Bill The Sojourner rover was the first space exploration rover to successfully reach another planet. ... THEMIS in orbit The THEMIS mission uses a constellation of five NASA satellites to study energy releases from Earths magnetosphere known as substorms, magnetic phenomena that intensify auroras near Earths poles. ... PLC & input/output arrangements A Programmable Logic Controller, PLC, or Programmable Controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. ...

MCS-85 Family:

The 8085 CPU was only one part of a much larger family of chips developed by Intel, to build a complete system with. Although the 8085 CPU itself was not a great success (descendants of) many of these support chips later found their use in combination with the 8086 microprocessor, and are still in use today, although not as the chips themselves, but with their equivalent functionality embedded into larger VLSI chips, namely the "Southbridge" chips of modern PC's. The 8086 is a 16-bit microprocessor chip designed by Intel in 1978, which gave rise to the x86 architecture. ... It has been suggested that VHSIC be merged into this article or section. ... This article does not cite any references or sources. ...

  • 8085-CPU
  • 8155-RAM+ 3 I/O Ports+Timer
  • 8156-RAM+ 3 I/O Ports+Timer
  • 8185-SRAM
  • 8202-Dynamic RAM Controller
  • 8203-Dynamic RAM Controller
  • 8205-1 Of 8 Binary Decoder
  • 8206-Error Detection & Correction Unit
  • 8207-DRAM Controller
  • 8210-TTL To MOS Shifter & High Voltage Clock Driver
  • 8212-8 Bit I/O Port
  • 8216-4 Bit Parallel Bidirectional Bus Driver
  • 8218/8219-Bus Controller
  • 8222-Dynamic RAM Refresh Controller
  • 8226-4 Bit Parallel Bidirectional Bus Driver
  • 8231-Arithmetic Processing Unit
  • 8232-Floating Point Processor
  • 8237-DMA Controller
  • 8251-Communication Controller
  • 8253-Programmable Interval Timer
  • 8254-Programmable Interval Timer
  • 8255-Programmable Peripheral Interface
  • 8256-Multifunction Support Controller
  • 8257-DMA Controller
  • 8259-Programmable Interrupt Controller
  • 8271-Programmable Floppy Disk Controller
  • 8272-Single/Double Density Floppy Disk Controller
  • 8273-Programmable HDLC/SDLC Protocol Controller
  • 8274-Multi-Protocol Serial Controller
  • 8275-CRT Controller
  • 8276-Small System CRT Controller
  • 8278-Programmable KeyBoard Interface
  • 8279-KeyBoard/Display Controller
  • 8282-8-bit Non-Inverting Latch with Output Buffer
  • 8283-8-bit Inverting Latch with Output Buffer
  • 8291-GPIB Talker/Listener
  • 8292-GPIB Controller
  • 8293-GPIB Transceiver
  • 8294-Data Encryption/Decryption Unit+1 O/P Port
  • 8295-Dot Matrix Printer Controller
  • 8296-GPIB Transceiver
  • 8297-GPIB Transceiver
  • 8355-16,384-bit (2048 x 8) ROM with I/O
  • 8604-4096-bit (512 x 8) PROM
  • 8702-2K-bit (265 x 8 ) PROM
  • 8755-EPROM+2 I/O Ports

Educational Use

In many engineering schools in Iran, India, Brazil, Mexico, Germany, Greece, Panama, Nepal and Malaysia, the 8085 processor is popularly used in many introductory microprocessor courses.


8085 Simulators exist aplenty for educational use. One such, is the GNUSim8085 [4], which works on GNU/Linux.

  Results from FactBites:
The Intel 8085 (217 words)
The 8085 was the follow-on processor to the very successful Intel 8080A processor.
The 8085 incorporated all the features of the 8224 (clock generator) and the 8228 (system controller) increasing the level of system integration.
The 8085 family is also referred to as the MCS-85.
Intel 8086 (593 words)
Shortly later the Intel 8088 was introduced with an external 8-bit bus, allowing the use of cheap chipsets.
It was based on the design of the 8080 and 8085 (it was Assembly language source compatible[?] with the 8080) with a similar register set, but was expanded to 16 bits.
Intel bubble memory was on the market for a while, but faded away as better and cheaper memory technologies arrived.
  More results at FactBites »



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