The SCSI adapter is a bus master device which gains control of the PCI bus to transfer data between the CPU memory and the SCSI devices. The I/0 base address and interrupts are set by the PCI plug and play BIOS at boot time.

A SCSI configuration utility is available on boot-up of the board. Shortly after the SCSI BIOS information displays, the configuration program can be accessed by pressing Control C. The configuration utility will allow you to scan the SCSI bus, change configuration options, and view a list of SCSI devices connected to the board. If the SCSI BIOS is inadvertently turned off in the SCSI configuration utility, turn it back on by holding <CTRL> A when the board is reset.

The Symbios SCSI adapter on the TX Series Board supports:

• SCSI 8 bit (narrow) - Devices 0-6 on J14 with a 50-pin standard ribbon cable.
• SCSI 16 bit (wide) - Devices 0-6 and 8-15 on J18 with a 68-pin high density ribbon connector

On-board SCSI termination is controlled by dip switches 4 and 5 of switch S2. Normally, both switches are off, which terminates the high and low order bits of the SCSI bus.

The following four diagrams show the switch settings for proper SCSI termination with SCSI devices connected to connectors J14 (50 pin) or J18 (68 pin).

Figure 3-1, 8 Bit External OR Internal SCSI devices

Figure 3-2, 8 Bit Internal AND External SCSI devices

Figure 3-3, 16 Bit Internal OR External SCSI devices

Figure 3-4, 16 Bit Internal AND External SCSI devices

Note: Termination should also be configured as "enabled" if the SCSI interface is not used. The last device on the SCSI cable must also supply a termination load to the cable. SCSI devices not at the end of the cable must have their termination loads disconnected. Enabling and disabling a SCSI device's termination may involve a switch or shunt setting or the installation or removal of resistive SIP or DIP packages on their circuit board. Consult the installation manual for the SCSI device to determine its termination options.