Digital Electronics: Principles, Devices and Applications

Microprocessors 527A 15Address BusA 08085microprocessorRAMROMD 7Data BusD 0Clk—–RD—–WR—––RESINTRIO/M}OutputInterfaceInputInterfaceOutputDeviceInputDeviceFigure 13.2Bus interface between the microprocessor and its peripheral devices.In most of these systems, the microprocessor, memory and I/O ports are combined onto one chip,known as the microcontroller. Microcontrollers are discussed in detail in Chapter 14.13.2 Evolution of MicroprocessorsThe evolution of microprocessors has been known to follow Moore’s law, which suggests that thecomplexity of an integrated circuit, with respect to the minimum component cost, doubles every 24months. This rule has been generally followed, since the humble beginning of microprocessors as thedrivers for calculators to the present-day scenario where every system, from the largest mainframes tothe smallest handheld computers, uses a microprocessor at its core.The first microprocessor was introduced in 1971 by the Intel Corporation. It was a four-bitmicroprocessor, Intel 4004. Other four-bit microprocessors developed were Intel 4040 by Intel, PPS-4by Rockwell International, T3472 by Toshiba and so on. The first eight-bit microprocessor, named Intel8008, was also developed by Intel in the year 1972. All these microprocessors were made using PMOStechnology. The first microprocessor using NMOS technology was Intel 8080, developed by Intel in the