Assembly Language Help (alang.hlp) (Table of Contents; Topic list)
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Int 15h Function C4h
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     This function is available only on machines using the Micro
     Channel Architecture (MCA) bus.
 
     After a slot is enabled with Subfunction 01h, specific information
     can be obtained for the adapter in that slot by performing port
     input operations:
 
     Port     Function
 
     100h     MCA ID (low byte)
     101h     MCA ID (high byte)
     102h     Option Select Byte 1
              (bit 0 = 1 if enabled, = 0 if disabled)
     103h     Option Select Byte 2
     104h     Option Select Byte 3
     105h     Option Select Byte 4
              (bits 6-7 = channel check indicators)
     106h     Subaddress Extension (low byte)
     107h     Subaddress Extension (high byte)
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