Device Identification

Device Identification

1. Multiple interrupt lines

   • Most straightforward approach to the problem.
   • Between the processor and the I/O modules
   • Likely that each line will have multiple I/O modules

2. Software Poll

   • Branches to an interrupt-service routine
   • To poll each I/O module to determine which module caused the interrupt
   • Disadvantage : Time Consuming

3. Daisy Chain

   • Uses a hardware poll
   • Signal propagates through the series of I/O modules until gets to requesting module
   • Requesting module responds by placing a vector on data lines
   • Vector : The address of the I/O module and some other unique identifiers
   • Vector Interrupt : Processor uses vector as a pointer to the appropriate device-service routine to avoid the need to execute a general interrupt-service routine first

4. Bus Arbitration

   • I/O module must first gain control of the bus before raising the interrupt service line
   • Responds on the interrupt acknowledge line
   • Requesting modules then places its vector on data lines