The Z5380 SCSI (Small Computer System Interface) controller is designed to implement the SCSI protocol as defined by the ANSI X3.131-1986 standard, and is fully compatible with the industry standard 5380. It is capable of operating both as a Target and as an Initiator. Special high-current open-drain outputs enable the Z5380 to directly interface to, and drive, the SCSI bus. The Z5380 has the necessary interface hook-ups which allows the system CPU to communicate with it like any other peripheral device. The CPU can read from, or write to, the SCSI registers which are addressed as standard or memorymapped I/Os (Figure 1). The Z5380 increases the system performance by minimizing the CPU intervention in DMA operations which the SCSI controls. The CPU is interrupted by the SCSI when it