Digital Electronics: Principles, Devices and Applications

Microprocessors 563from the main memory and keeping track of the display position of the screen. One of the commonlyused programmable CRT controllers is Intel’s 8275H. It allows a simple interface to almost any rasterscan CRT display with minimum external hardware and software overheads. The number of displaycharacters per row and the number of character rows per frame are software programmable.13.14.9 Floppy Disk ControllerThe floppy disk controller is used for disk drive selection, head loading, the issue of read/writecommands, data separation and serial-to-parallel and parallel-to-serial conversion of data. Examples offloppy disk controllers include Intel’s 82078, 82077 and 8272.13.14.10 Clock GeneratorThe clock generator is a circuit that produces a timing signal for synchronization of the circuit’soperation. Examples of clock generators used in microprocessor systems include 8284 and 82284.8284 generates the system clock for the 8086 and 8088 processors. It requires a crystal or a TTLsignal source for producing clock waveforms. It provides local READY and MULTIBUS READYsynchronization.82284 is a clock generator/driver that provides clock signals for the 80286 processor and supportcomponents. It also contains logic to supply READY to the CPU from either asynchronous orsynchronous sources and synchronous RESET from an asynchronous input with hysteresis. The 82284is packaged in 18-pin DIP and contains a crystal-controlled oscillator, an MOS clock generator, aperipheral clock generator, multibus ready synchronization logic and system reset generation logic.13.14.11 Octal Bus TransceiverBus transceivers are devices with a high-output drive capability for interconnection with data buses.In a microprocessor-based system they provide an interface between the microprocessor bus and thesystem data bus. 8286 is an eight-bit bipolar transceiver with a three-state output that is used in a widevariety of buffering applications in microcomputer systems. It comes in a 20-pin DIP package.Review Questions1. Briefly describe the difference between a microprocessor and a microcomputer. What are the threemain constituents of a microprocessor and what is the basic function performed by each one ofthem.2. What are the different types of register found in a typical microprocessor? Briefly describe thefunction of each one of them.3. Distinguish between the following(a) address bus and data bus;(b) direct addressing mode and indirect addressing mode;(c) programmable timer and clock generator;(d) programmable interrupt controller and DMA controller;(e) RISC and CISC microprocessors.