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Intel 8085 AI simulator
(@Intel 8085_simulator)
Hub AI
Intel 8085 AI simulator
(@Intel 8085_simulator)
Intel 8085
The Intel 8085 ("eighty-eighty-five") is an 8-bit microprocessor produced by Intel and introduced in March 1976. It is 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 four new interrupt pins and 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 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 via two 8-bit pathways, and one of those two has to be temporarily latched using separate hardware such as a 74LS373. 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 late 1970s and early 1980s, which took over much of the desktop computer market.
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.
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 eight bits of the 16-bit address bus to limit the number of pins to 40. State signals are provided by dedicated bus control signal pins and two dedicated bus state ID pins named S0 and S1. Pin 40 is used for the power supply (+5 V) and pin 20 for ground. Pin 39 is used as the Hold pin.
The Intel 8085 processor was designed using nMOS circuitry, with later "H" versions implemented in Intel's enhanced nMOS process known as HMOS II ("High-performance MOS"), which was originally developed for fast static RAM products. Unlike the 8080, the 8085 requires only a single 5-volt power supply, similar to its competing processors. The 8085 contains approximately 6,500 transistors.
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.
Intel 8085
The Intel 8085 ("eighty-eighty-five") is an 8-bit microprocessor produced by Intel and introduced in March 1976. It is 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 four new interrupt pins and 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 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 via two 8-bit pathways, and one of those two has to be temporarily latched using separate hardware such as a 74LS373. 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 late 1970s and early 1980s, which took over much of the desktop computer market.
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.
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 eight bits of the 16-bit address bus to limit the number of pins to 40. State signals are provided by dedicated bus control signal pins and two dedicated bus state ID pins named S0 and S1. Pin 40 is used for the power supply (+5 V) and pin 20 for ground. Pin 39 is used as the Hold pin.
The Intel 8085 processor was designed using nMOS circuitry, with later "H" versions implemented in Intel's enhanced nMOS process known as HMOS II ("High-performance MOS"), which was originally developed for fast static RAM products. Unlike the 8080, the 8085 requires only a single 5-volt power supply, similar to its competing processors. The 8085 contains approximately 6,500 transistors.
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.
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