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The Intel 8085 ("''eighty-eighty-five''") is an 8-bit microprocessor produced by Intel and introduced in 1976.〔http://www.intel.com/pressroom/kits/quickrefyr.htm#1976〕 It is software-binary compatible with the more-famous Intel 8080 with only a few minor instructions added. However, it requires less support circuitry, allowing simpler and less expensive microcomputer systems to be built. The "5" in the part number highlighted the fact that the 8085 uses a single +5-Volt (V) power supply by using depletion mode transistors, rather than requiring the +5 V, −5 V and +12 V supplies needed by the 8080. This brought it up with the competing Z80, a popular 8080-derived CPU introduced the year before. These processors could be used in computers running the CP/M operating system. The 8085 is supplied in a 40-pin DIP package. To maximise the functions on the available pins, the 8085 uses a multiplexed address/data bus. However, an 8085 circuit requires an 8-bit address latch so Intel manufactured several support chips with an address latch built in. These include the 8755, with an address latch, 2 KB of EPROM and 16 I/O pins, and the 8155 with 256 bytes of RAM, 22 I/O pins and a 14 bit programmable Timer/Counter. The multiplexed address/data bus reduced the number of PCB tracks between the 8085 and such memory and I/O chips. Both the 8080 and the 8085 were eclipsed by the Zilog Z80 for desktop computers, which took over most of the CP/M computer market as well as a share of the booming home computer market in the early-to-mid-1980s. The 8085 had a long life as a controller. Once designed into such products as the DECtape controller and the VT102 video terminal in the late 1970s, it served for new production throughout the lifetime of those products. This was typically longer than the product life of desktop computers. ==Description== The 8085 is a conventional von Neumann design based on the Intel 8080. Unlike the 8080 it does not multiplex state signals onto the data bus, but the 8-bit data bus is instead multiplexed with the lower part of the 16-bit address bus to limit the number of pins to 40. Pin 40 is used for the power supply (+5 V) and pin 20 for ground. Pin 39 is used as the Hold pin. Pins 15 to 8 are generally used for address buses. 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 single 5 volt power supply is needed, like competing processors and unlike the 8080. The 8085 uses approximately 6,500 transistors.〔The history of the microcomputer-invention and evolution, S Mazor - Proceedings of the IEEE, 1995〕 The 8085 incorporates the functions of the 8224 (clock generator) and the 8228 (system controller) on chip, increasing the level of integration. A downside compared to similar contemporary designs (such as the Z80) is the fact that the buses require demultiplexing; however, address latches in the Intel 8155, 8355, and 8755 memory chips allow a direct interface, so an 8085 along with these chips is almost a complete system. The 8085 has extensions to support new interrupts, with three maskable vectored 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 permits simple systems to avoid the cost of a separate interrupt controller. Interrupts are enabled by the EI instruction and disabled by the DI instruction. Like the 8080, the 8085 can accommodate slower memories through externally generated wait states (pin 35, READY), and has provisions for Direct Memory Access (DMA) using HOLD and HLDA signals (pins 39 and 38). An improvement over the 8080 is 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). The 8085 is a binary compatible follow up on the 8080, using the same basic instruction set as the 8080. Only a few minor instructions were new to the 8085 beyond the 8080 set. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Intel 8085」の詳細全文を読む スポンサード リンク
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