Specifications

Hardware Configuration
2–23
be re-mapped to 140h-15Fh by installing a shunt on W24. The SCSI BIOS extensions of the ROM
BIOS do not support the alternate I/O address range.
Interrupt Request Assignment
The SCSI interface, supported by the SCSI BIOS extensions of the ROM BIOS does not use an
interrupt. However, some operating systems, such as OS/2 and Windows95, and Adaptec ASPI
drivers require IRQ11. This is the default assignment, implemented on jumper W12. A shorting
block installed on W12 connects the SCSI interface to IRQ11. If you use DOS and the internal SCSI
support firmware, you can remove the jumper and use IRQ11 for another peripheral.
Active Terminators
The SCSI interface uses “active terminators” for the SCSI bus. Active terminators draw less current
than 330/220 ohm terminators (the normal method of SCSI line termination), and are less susceptible
to noise.
Only the SCSI devices on each end of the SCSI bus should be terminated. Enable or disable the SCSI
terminators on the Little Board/486i using SETUP. Refer to the section describing SETUP in Chapter
3 for details.
External Termination Power Option
You can power external SCSI terminations from the Little Board/486i. A jumper option (W3),
connects power (+5V) to the SCSI bus TERMPWR signal (J9, pin 26). The board includes a Schottky
protection diode to prevent damage to the board by current flowing from the SCSI bus.
The default jumpering of W3 is open; that is, termination power is not normally supplied by the Little
Board/486i.
SCSI ID
Every SCSI device must be configured for a specific SCSI bus ID, between 0 and 7. Normally, set the
SCSI initiator ID to 7. Set disk drive and other SCSI target device IDs to 0 – 6. Set the SCSI initiator
ID using SETUP. Details are provided in the SETUP section of Chapter 3.
Enabling or Disabling the SCSI Disk Interface
To enable the SCSI hardware, install W25. Removing W25 disables the SCSI sub-system. Using
SETUP, disable or enable the SCSI BIOS disk drive services. Note that this SETUP option disables
access to the SCSI BIOS disk drive services only. The SCSI hardware can still function normally and
BIOS calls are still serviced. For instance, a CD ROM drive (with its driver) would still function
normally. Disabling the SCSI BIOS might be desirable for several reasons:
! To speed system booting when you don’t use SCSI. Otherwise, there is a delay while the system
waits for a non-existent SCSI device to respond to initialization commands.
! To disable SCSI BIOS control of the SCSI hardware, when you have a non-standard use for the
interface, implemented by a device driver.
Details about the SCSI interface, installing a SCSI hard disk, and using SETUP to configure the SCSI
interface are provided in Chapter 3.
2.11 BYTE-WIDE SOCKETS
The Little Board/486i has two 32-pin on-board byte-wide memory sockets, designated S0 and S1.
These sockets can accept a wide variety of EPROM, Flash EPROM, SRAM, and nonvolatile RAM