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Unformatted text preview: 51 Chapter 6 Interfacing Concepts Interfacing is the process of connecting devices together so that they can exchange information. A special interface must translate between the signal that the computer uses and those that the peripheral uses. An interface includes the physical connection, the hardware and a set of rules or procedures, i.e., the software. The interface must provide the proper timing and control. Formally, an interface is a device and/or set of rules to match the output of one device to the input of another device for sending information from one to the other. For example, the connection between a microprocessor and external memory is an interface. There are physical connections for addressing, data flow and control signals. The software consists of instructions that read from and/or write to an addressed location. The major problems with interfacing are: - wide variety of peripheral devices - enormous range of peripheral speeds - variety in signal types and signal levels in peripheral devices - complexity of the signaling structure (strobes, handshaking, etc.) Basic Input/Output Interfacing The process of getting signals in and sending signals out is called input/output (I/O). The subsystems responsible for this task are known as I/O subsystems , which are sometimes called an interface . Input and output are similar to memory accesses. The processor can transfer data to and from the peripherals in the same way that it transfers data to and from memory. In fact, memory is simply another peripheral. I/O direction is relative to the MCU. Input is data read by the MCU. Output is data sent out by the MCU. A simple I/O section in a microcomputer system may include a temperature sensor that provides data every 5 minutes, a modem device that transfers 56K bits every second and a floppy disk that transfers bits in the order of megabits per second. Simple Input Interface An input operation is similar to a memory read cycle. 1. μ P generates address and control signals to select the input device. 2. Input device generates data and loads data lines. 3. μ P reads data from the data bus and places it in a register. Most μ Ps accept data from an input device through the data bus connections and therefore require some form of switch to connect this data to the bus at the appropriate time. One effective digital switch available is the three-state buffer . Example : Eight On/Off switches can be connected to the CPU by the use of a three-state buffer as follows: Device Decoder +5v R +5v R to μ P data bus INSTROBE from μ P address bus 74LS244 52 INSTROBE is the timing control signal. Device decoder generates the INSTROBE signal for the required input device....
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This note was uploaded on 01/30/2011 for the course EE 447 taught by Professor Skst during the Fall '10 term at Middle East Technical University.
- Fall '10