MICROPROCESSOR 8085
The Intel 8085 ("eighty-eighty-five") is an 8-bit microprocessor introduced by Intel in 1977. The 8085 is a conventional von Neumann design based on the Intel 8080. It is designed by using nmos technology. The "5" in the model number came from the fact that the 8085 requires only a +5-Volt (V) power supply. rather than requiring the +5 V, −5 V and +12 V supplies the 8080 needed. It has an 8-bit data bus and a 16-bit address bus. it can work up to 5 MHz frequency. It has 40 pins in its chip. The lower order address bus is multiplexed with a data bus to minimize the chip size.
The 8085 has extensions to support new interrupts, with 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 that permitted simple systems to avoid the cost of a separate interrupt controller.
The 8085 is supplied in a 40-pin DIP package. To maximize 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, no doubt thanks to its built-in serial I/O and 5 prioritized interrupts, arguably microcontroller-like features that the Z80 CPU did not have. Once designed into such products as the DECtape controller and the VT102 video terminal in the late 1970s, the 8085 served for new products throughout the lifetime of those products. This was typically longer than the product life of desktop computers.
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