Specifications
To enable
the
SCSI halt mode, install shorting
jumpers
at
WI
and W6
on
the
Little
Board/PC.
WI
is located between
Ul
and SIMM2;
W6
is located between U2
and
U6 (refer
back to
FtgUl'e
2-1). When these
two
jumpers are left
off,
SCSI Halt Mode is disabled. The
default configuration, as shipped,
is SCSI Halt Mode disabled.
Alternate DMA Channel Option
The SCSI interface can be configured to use either DMA channel 1
or
3 for
data
transfer
control. DMA Channel 3 corresponds to a standard
PC's
fixed
disk adapter, and is used as
the default by the board's SCSI/BIOS. You can alter these assignments relative to the
de-
faults, but this will sacrifice SCSI/BIOS and SCSI utilities compatibility. These SCSI inter-
face conftgUl'ation options are shown in Table
2-24.
Table 2-24.
SCSI
Interface Option Jumpers
JUMPER
SIGNAL
FUNCTION
W1
PCTC
Connects
DNA
END
(TC)
signal
to
53C80's
-EOP
input.
Default: unshorted.
W2-1
DRQ3
DNA
request chamel option.
W2-2
DRQ
from
53C80
Default: 1/2
(DRQ3),
via
a
trace.
W2-3
DRQ1
(W2-1
is
at
top.)
W3-1
DACa
DNA
acknowledge
chamel option.
W3-2
DACK
to
53C80
Default: 1/2 (DACa),
via
a trace_
W3-3
DACK1
(W3-1
is
at
top.)
W4
Term
Power
Provides
+5
volts
termination
power
to
pin
26
of the
SCSI
Bus.
Default: unshorted.
W6
53C80
IRQ
Connects 53C80's
interrupt
output
to
PC
bus
IRQ5.
Default: unshorted
No
termination
power
protection diode
is
provided
on
the
board.
W4
nust
NOT
be
installed
if
any
other
bus
device supplies
termination power, or board
damage
may
result!
2-25