Byte Description Meaning10 Disconnection Option Each bit corresponds to a SCSIdevice, e.g., bit 0 corresponds tothe device at SCSI address 0.When set to one, the hostadapter will prevent the SCSIdevice from disconnecting.11-FF Reserved (00)If the command completes normally, the HACC interrupt will be set to one. If themailbox area has not been properly initialized, all 17 bytes are still requested by thehost. If byte 4, the Number of Mailboxes, is zero, bytes 5-7 must be ignored.Initialize SCSI Subsystem (Operation Code 10)After receiving this command, the host adapter expects one byte from the host to con-figure the SCSI bus.Enable/Disable Disconnect/ReconnectEnable/Disable Synchronous NegotiationEnable/Disable SCSI Bus ParityReturn Firmware Checksum (Operation Code 11)After receiving this command, the host adapter passes two bytes to the host which re-flect the checksum of the Standard Mode micromode. Note that this checksum is notmarked on the board. The checksum on the EEPROM reflects an aggregate of the En-hanced Mode, Standard Mode and download utility microcodes.Write Adapter Channel 2 Buffer (Operation Code 1A)After receiving this command, the host adapter expects three outbound informationbytes to be transferred which point to an area of 64 bytes in system RAM. The areapointed to will be transferred to the host adapter’s channel 2 buffer using the hostadapter’s DMA circuitry. After completing the transfer of the 64 bytes from the indi-cated buffer area to the host adapter, the HACC interrupt will be set indicating nor-mal completion. This command is used in conjunction with the Read Channel 2Buffer command for host adapter diagnostics. The channel 2 buffer is used for trans-mission of all information except the actual data field between the host adapter andthe host system.Byte 0 Buffer area address, Most significant byteByte 1 Buffer area addressByte 2 Buffer area address, Least significant byteadaptec AHA-1740A/1742A/17445-12
