Function Of I/O Modules

By : ATHIRAH BT ZAHARUDIN

The Function Are :

1)   Control and Timing.

2)   CPU Communicating.

3)   Device Communication.

4)   Data Buffering.

5)   Error Detection.

1)   Control and Timing

•     Required because of multiple devices all communicating on the same channel
•         Example :-

–CPU checks I/O module device status

–I/O module returns status

–If ready, CPU requests data transfer

–I/O module gets data from device

–I/O module transfers data to CPU

–Variations for output, DMA, etc.

2)   CPU Communicating

•      Commands from processor – Examples: READ SECTOR, WRITE SECTOR, SEEK track number, and SCAN record ID.

•        Data – passed back and forth over the data bus

•        Status reporting – Request from the processor for the I/O Module's status.  May be as simple as BUSY and READY

•        Address recognition – I/O device is setup as a block of one or more addresses unique to itself

3)   Device Communication.

•    Specific to each device

4)   Data Buffering.

•    Due to the differences in speed (device is usually orders of magnitude slower) the I/O module needs to buffer data to keep from tying up the CPU's bus with slow reads or writes

5)   Error Detection.

•        simply distributing the need for watching for errors to the module They may   include:

               - Malfunctions by device (paper jam)              

                      - Data errors (parity checking at the device level)            

                      - Internal errors to the I/O module such as buffer overruns