Mailbox Count. If the Mailbox Count is zero, the INVDCMD bit will be set withHACC to indicate that the parameter is invalid.At command completion, HACC will be set to one and INIT will be reset to zero.HACC will be reset as specified in the Interrupt Flag Port section of Chapter Four,Hardware Functional Description.Start SCSI Command (Operation Code 02)This command indicates that the host has made at least one Mailbox Out entry andthat the host adapter should begin to scan for active MBO entries. Once scanning hasbeen started, it continues until all MBO entries have been serviced, either by begin-ning the requested operations or by queuing the activities for later execution. Sinceit is not easy for the host to determine that scanning is still taking place, the hostshould normally issue this command every time a Mailbox Out is filled. This com-mand does not require additional data bytes. To avoid unnecessary interrupts, HACCis NOT set after command completion. HACC will be set with INVDCMD if the mail-box was not yet initialized.Start PC AT BIOS Command (Operation Code 03)This command is used by the Adaptec BIOS to communicate with the host adapterfirmware. The command is not available for use by programs other than the AdaptecBIOS.Adapter Inquiry (Operation Code 04)After receiving this command, the host adapter returns four bytes of data describingthe host adapter firmware revision level. After completing the transfer of the fourbytes of inbound data, the HACC interrupt is set indicating normal command comple-tion. The bytes contain the following information:Byte Description Value Meaning00 Board Identification (ID)The value in this byte allowssoftware supported on both thePC AT and on the MicroChannel to distinguish the typeof supporting host adapter.00h Board is an AHA-1540 with 16-Head BIOS30h (’0’ ASCII) Board is an AHA-1540 with 64-Head BIOS41h (’A’ ASCII) Board is an AHA-1540/1542, 64-Head BIOS42h (’B’ ASCII) Board is an AHA-1640, 64-Head BIOS43h (’C’ ASCII) Board is an AHA-1740A/1742A/1744All Others ReservedContinuedEISA-to-Fast SCSI Host Adapter Standard Mode Firmware Description5-3
