I/O Organization

1. I/O Organization popo

2. I/O Organization • 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 popo

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 popo

4. I/O Organization • Accessing I/O • Single bus structure to connect I/O popo

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 popo

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 popo

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 popo

8. I/O Organization popo

9. I/O Organization • 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 popo

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 popo

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 popo

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. popo