Bios Driver Needs; Scsi Subsystem Configuration; Initialize Scsi Subsystem Command (Standard Mode); Initialize Scsi Subsystem Command (Enhanced Mode) - Adaptec AHA-1740A Technical Reference Manual

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BIOS Driver Needs

At power-on time the BIOS needs information about the SCSI bus to aid in minimum
power-on time and confidence in a complete working system. The information given
tells the BIOS that a device is, or is not, installed; if intalled and a selection error oc-
curs, to wait for no error, or report the error after a timeout; if installed and a selec-
tion error occurs, to not report the error and continue with power-on initialization.

SCSI Subsystem Configuration

Due to a limitation of the hardware, there are only a few registers that may be
loaded at power-up time. Some information not directly controlling hardware may be
loaded independently of the normal EISA Configuration program that runs at power-
on time. The BIOS will program the AHA-1740 on power-up using the Initialize SCSI
Subsystem command with this additional information. The hardware configuration
registers will still be programmed by the configuration program. The definition of the
command and data structure follows.

Initialize SCSI Subsystem Command (Standard Mode)

The command to initialize the SCSI Subsystem in Standard Mode is an additional
host adapter command. This command is sent in the normal manner described in the
AHA-1540 manual using the LAVAIL status bit in the status register. The command
byte (10h) is followed by one data byte which describes the global setting of parity en-
able, synchronous transfer, and disconnection. The definition is as follows:
Bit Definition
7 Reserved (set to 0)
6 Reserved (set to 0)
5 Enable parity check
4 Reserved (set to 0)
3 Enable synchronous transfer
2 Enable Disconnection
1 Reserved (set to 0)
0 Reserved (set to 0)

Initialize SCSI Subsystem Command (Enhanced Mode)

The command to initialize the SCSI Subsystem is a standard 48-byte command using
the AHA-1740 I/O interface. The definition of the command is given in Chapter Six,
Enhanced Mode Firmware Description.
FlagWord 1 Options
Disable Status Block (bit 14) is supported. Setting this bit will disable the writing of
the termination status block if no error occurs. All other bits should be set to zero.
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AHA-1740A/1742A/1744