Chapter 6: Input/Output

Chapter 6: Input/Output

1. EXTERNAL DEVICES

   • Human readable
     • -Communicating with computer users
   • Machine readable
     • Communicating with equipment
   • Communication
     • -Suitable for communicating with remote devices such as a terminal, a machine readable device or another computer
   • Attach to the computer by a link to an I/O module

2. Major functions of an I/O module

   • -Control and timing
   • Processor communication
   • Device communications
   • Data buffering
   • Error detection

3. PROGRAMMED I/O

   • -Data are exchanged between the processor and the I/O module
   • INTERRUPT-DRIVEN I/O
     • -Processor issues an I/O command, continues to execute other instructions, and is interrupted by the I/O module when the latter has completed its work
   • DIRECT MEMORY ACCESS(DMA)
     • -The I/O module and main memory exchange data directly without processor involvement

4. I/O COMMANDS

   • Control
     • -Used to activate a peripheral
   • Test
     • -Used to get various status conditions associated with an I/O module
   • Read
     • -Causes he I/O module to obtain an item of data from the peripheral and place it in an internal buffer
   • Write
     • -Causes the I/O module to take an item of data from the peripheral and place it in and internal buffer

5. I/O MAPPING SUMMARY

   • ISOLATED I/O
     • -Separate address spaces
     • -Special commands for I/O
   • MEMORY MAPPED I/O
     • -Devices and memory share an address space
     • -I/O looks like memory read/write
     • -No special commands

6. DEVICE IDENTIFICATION

   • SOFTWARE POLL
     • -Poll each I/O module to determine which module caused the interrupt
   • MULTIPLE INTERRUPT LINES
     • -Each line will have multiple I/O modules attached to it
   • DAISY CHAIN
     • -Vector- Address of the I/O module or some other unique identifier
   • BUS ARBITRATION
     • -An I/O module must first gain control of a bus before it can raise the interrupt request line