W10_18_IO3_Interface

W10_18_IO3_Interface - 18 I/O and Peripherals Part 3: I/O...

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18 I/O and Peripherals Part 3: I/O Interfaces CSC 230 1
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Input / Output: or general ability to exchange data ± I/O refers to transmission of data from one device (sender) to another (receiver) ± I/O operations require controls to coordinate the operation of the sender and receiver Control information NEED: DATA to transmit Processor Memory Typical information includes: Bus -readytosend -c leartosend - ata received 2 I/O device 1 I/O device n data received - errors
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I/O interface for an input device Bus Address lines Data lines Control lines Address decoder Control circuits Data and Status registers I/O interface INPUT DEVICE 3
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I/O Control Alternatives Processor initiated Device initiated nterrupt nconditional onditional Interrupt transfer Unconditional transfer Conditional transfer Polling DMA access 4 handshake protocols
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I/O Control Alternatives (1): Processor initiated Processor (CPU) initiates transfer (program controlled) nconditional onditional unconditional device must always accept conditional CPU checks if device accepts Examples: isplaying Hand-shaking ¾ displaying results on LEDs ¾ reading a set of switches Interchange of control information between the processor and a device to nsure oth are ready r an 6 ensure both are ready for an I/O transfer
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I/O Control Alternatives (2): Device initiated Device initiates transfer olling (programmed) ± device sends an terrupt signal Interrupt driven Polling (programmed) ± device posts a flag signal in interrupt signal Î it tells the processor to transfer data some location to state that data is ready to be transferred e rocessor to/from the device ± the processor checks it periodically 7
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Sampling the status of an external device which is repeatedly checked for readiness (by checking some posted signal) olling n I/O device can be seen as either a form f: Polling an I/O device can be seen as either a form of: 1. processor- initiated transfer 2. or device initiated transfer VIEW 1: A. the program/processor decides when the transfer hould take place VIEW 2: I. device posts a “flag” to denote that it needs to ansfer data should take place B. processor periodically “polls” each device in turn and checks status efore ontinuing with transfer data II.processor periodically “polls” each device in turn and checks before continuing with transfer ± conditional or unconditional
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This note was uploaded on 01/15/2012 for the course CSC 230 taught by Professor Jasond.corless during the Summer '11 term at University of Victoria.

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W10_18_IO3_Interface - 18 I/O and Peripherals Part 3: I/O...

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