Chapter FiveStandard Mode Firmware DescriptionHost Adapter Command OverviewStandard Mode is the mode in which the AHA-1740A/1742A/1744 can operate in or-der to run existing software for earlier Bus Master host adapters. In Standard Mode,the AHA-1740A/1742A/1744 supports two types of commands: SCSI and adapter com-mands. SCSI commands are issued using the mailbox protocol and a Command Con-trol Block (CCB). When SCSI commands are used, the AHA-1740A/1742A/1744 isoperating in true multithreading mode. In this mode of operation, the AHA-1740A/1742A/1744 is capable of executing multiple commands for multiple targetsconcurrently. The AHA-1740A/1742A/1744 maximizes the I/O transaction through-put by managing SCSI disconnection and reconnection.Adapter commands are issued by writing to the Command/Data Out port and mostcommands cannot be issued when there are outstanding SCSI commands. Adaptercommands are used to initialize the host adapter and to establish control conditionswithin the host adapter. Adapter commands are also used to transmit the special pa-rameters for communication between the BIOS and the host adapter for the execu-tion of Interrupt 13 operations.Following is a list of the adapter command operation codes (hex):Code Command00 No Operation01 Mailbox Initialization02 Start SCSI Command*03 Start PC AT BIOS Command04 Adapter Inquiry05 Enable Mailbox Out Available Interrupt*06 Set Selection Time Out07 Set Bus-On Time08 Set Bus-Off Time09 Set Transfer Speed0A Return Installed Devices0B Return Configuration Data0C Enable Target Mode0D Return Setup Data10 Initialize SCSI Subsystem11 Return Firmware Checksum1A Write Adapter Channel 2 Buffer1B Read Adapter Channel 2 Buffer1C Write Adapter FIFO Buffer1D Read Adapter FIFO Buffer1F Echo Command Data5-1
