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I/O Organization. Accessing I/O The important parts of any computer system are, CPU, Memory & I/O devices (peripherals) CPU fetches instructions (opcodes.

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Presentation on theme: "I/O Organization. Accessing I/O The important parts of any computer system are, CPU, Memory & I/O devices (peripherals) CPU fetches instructions (opcodes."— Presentation transcript:

1 I/O Organization

2 Accessing I/O The important parts of any computer system are, CPU, Memory & I/O devices (peripherals) CPU fetches instructions (opcodes & operands) from memory, processes them and stores results in memory Other components called I/O system The main function of I/O system to transfer information between CPU or memory and outside world

3 I/O Organization Accessing I/O I/O devices cannot be connected directly to the system bus Because Different I/O with different methods of operation, so it would be impractical to incorporate to control a range of devices Data transfer rate of peripherals is often much slower than that of memory / CPU, so it would be impractical to use high speed system bus to communicate Different I/O with different data formats and word length that of CPU used To overcome all these difficulties, it is necessary to use a module in between system bus and I/O devices called I/O module or I/O system or I/O interface

4 I/O Organization Accessing I/O Single bus structure to connect I/O

5 I/O Organization Accessing I/O Single-bus structure The bus enables all the devices connected to it to exchange information Typically, the bus consists of three sets of lines used to carry address, data, and control signals Each I/O device is assigned a unique set of addresses

6 I/O Organization Accessing I/O The data bus lines are used to receive / send data from or to the I/O The address bus lines selects the I/O device for data transfer The control bus lines the direction of data flow

7 I/O Organization Accessing I/O I/O devices are accessed through I/O interface The major parts of I/O interface are 1 Control & Timing 2 CPU Communication 3 Device Communication 4 Data Buffering 5 Error Detection

8 I/O Organization

9 Accessing I/O Control & Timing To coordinate the flow of traffic b/w internal resources (memory, system bus) and external devices CPU Communication involves different types of signal transfers such as – Processor sends commands to the I/O, over control bus – Exchanges of data b/w processor & I/O, over data bus – Data transfer rate of I/O is often slower than the processor. So it is necessary to check the peripheral is ready or not for data transfer. If not processor must wait – No of peripheral devices may connected to the I/O interface. The I/O controls the communication of each peripherals with processor. So it must recognize one unique address of each peripheral

10 I/O Organization Accessing I/O Data buffering Data transfer rate of each peripheral devices are quite high than that of processor & memory The data coming from memory/processor are sent to I/O interface, buffered in I/O and sent to the peripheral device at its data rate Data are buffered in I/O interface so as not to tie up the memory in a slow transfer operation. I/O interface can able to operate at both peripheral & memory speed

11 I/O Organization Accessing I/O I/O interface is also responsible for error detection and reporting errors to the processor Type of errors are Mechanical Electrical malfunctions Bad disk Transmission error etc

12 I/O Organization Accessing I/O I/O interface consists of data register, status/control register, address decoder and external device interface logic. Data register holds the data being transferred to or from the processor Status/control register contains information relevant to the operation of I/O device Both data register & Status/control register connected to data Bus Address line drive the address decoder Address decoder enables the device to recognize its address when address appears on the address lines.


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