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EXCP

Indicates that the I/O-Error handler was entered due to an EXCEPTION. EXCP2 and EXCP1 (bits 18 and 17 of the PSW), and A17 (the MSB of the MAR, for a given memory size), indicate the type of exception.

The exception is determined from Table 3.

Table 3: Exceptions


     EXCP2   EXCP1    Explanation                         
       0       0      Divide by zero if A17 is low,       
                      Data Memory wrap-around if A17 is high  
       0       1      Arithmetic Overflow      
       1       0      Unsupported Opcode                  
       1       1      FASTBUS block transfer terminated due to    
                      a word count overflow


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A.Daviel,TRIUMF