The Intel 8085 is an 8-bit microprocessor produced by Intel and introduced in 1976. It is a software binary compatible with the more famous Intel 8080 with only two secondary instructions added to support its added interrupt and serial input / output characteristics. However, it requires less support circuitry, which makes it possible to build simpler and less expensive microcomputer systems.
The "5" in the part number highlighted the fact that the 8085 uses a single +5 volt (V) power supply using depletion mode transistors, instead of requiring +5 V, -5 V And +12 V required by the 8080. This capability matches that of the competition Z80, a popular CPU 8080 derivative introduced the previous year. These processors could be used on computers running the CP / M operating system.
The 8085 is supplied in a 40-pin DIP package. To maximize the functions on the available pins, the 8085 uses a multiplexed data / address bus. However, an 8085 circuit requires an 8-bit address block, so Intel manufactured several support chips with a built-in address lock. These include the 8755, with a blocking address, 2 KB of EPROM and 16 pins I / O and 8155 with 256 bytes of RAM, 22 pins I / O and a programmable timer / counter of 14 bits. The multiplexed address / data bus reduced the number of PCB tracks between 8085 and that memory and the I / O chips.
Both the 8080 and 8085 were overshadowed by the Zilog Z80 for desktops, which seized most of the CP / M computer market as well as a share of the growing home computer market in the early 1980s .
The 8085 had a long life as a controller, no doubt thanks to its built-in serial I / O and 5 prioritized interruptions, no doubt microcontroller-like features that the Z80 CPU did not have. Once designed in products such as the DECtape controller and the VT102 video terminal in the late 70's, the 8085 served for the new production over the life of those products. This was typically longer than the product life of desktop computers.