Intel 8085 (Microprocessor)

The Intel 8085 ("eighty-eighty-five") is an 8-bit microprocessor produced by Intel and introduced in March 1976. It is software-binary compatible with the more-famous Intel 8080. It is the last 8-bit microprocessor developed by Intel. The "5" in the part number highlighted the fact that the 8085 uses a single +5-volt (V) power supply, compared to the 8080's +5, -5 and +12V, which makes the 8085 easier to integrate into systems that by this time were mostly +5V. The other major change was the addition of a serial port, with separate input and output pins. This was often all that was needed in simple systems and eliminated the need for separate integrated circuits to provide this functionality, as well as simplifying the computer bus as a result. The only changes in the instruction set compared to the 8080 were instructions for reading and writing data using these pins. The 8085 is supplied in a 40-pin DIP package. Given the new serial pins, this required multiplexing 8-bits of the address (AD0-AD7) bus with the data bus. This means that specifying a complete 16-bit address requires it to be sent as two 8-bit values, and one of those two has to be temporarily stored, or latched, using separate hardware. 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. While the 8085 was an improvement on the 8080, it was eclipsed by the Zilog Z80 in the early-to-mid-1980s, which took over much of the desktop computer role. Although not widely used in computers, the 8085 had a long life as a microcontroller. Once designed into such products as the DECtape II controller and the VT102 video terminal in the late 1970s, the 8085 served for new production throughout the lifetime of those products.