I/O INTERRUPT AND ERROR HANDLER

The I/O-Error Handler is a program that is executed when the SSP is externally interrupted or encounters an error. Hardware-wise, entering the I/O-Error Handler does the following:

1. Stores the Processor Status Word (PSW) into DM 0.

2. Stores the Memory Address Register (MAR) into DM 4.

3. Sets the System Mask and Overflow Mask OFF; Disables Interrupts

4. Jumps to PM 0 and starts executing the I/O-Error Handler.

It is up to the I/O-Error Handler to determine what action to take in response to the I/O-Error. The reason that the I/O-Error Handler was entered can be decoded from the PSW and the MAR.