The A4091 is a full-length Zorro-III DMA Fast SCSI-2 hard drive controller designed for the A4000. It is based on the NCR 53C710 chip. (Editor's note: this is the same Fast SCSI controller chip used in the Warp Engine.)
Unlike some similar products, it is only a Fast SCSI-2 controller; it has no sockets for additional RAM. The A4091 package includes an active terminator and a custom ribbon cable, which is nicely folded to accommodate up to five internal drives, one on-board and a pair in each of the front and rear bays.
The A4091 requires a revision 11 Buster, which Commodore supplied loose with the card. It works with A3640 3.1 and 3.2 revisions, but not 3.0. [Editor's note: ROM revisions for the on-board ROM include 40.9 and 40.13.]
The board is theoretically capable of 10 megabytes per second transfer rates.
Board Layout
_________________________________________________________________ | ... ... LED ::::::::::::::: |___ | 50-Pin SCSI | | ||| ||| ||| Connector | | ||| ||| ||| ||| |# | ||| |||||| |# External | ||| ||| ||| ||| |||||| |# HiDensity | ||| ||| ||| ||| |||||| |# SCSI-2 | |||||| |# Connector | ||| ||| |# | ||| ||| ||| |=sw 8 | ||| . Power |= : | : Connector |= : |_________________________________________________________________|=sw 1 |||||||||||||||||||||||||||||| |LED Connectors
To DSPLY To MB
CN351
CN308
-------------------------
| o o o
o o o
|
| N R B
B R N
| C e l
l e C
|
d a a d
|
c c
|
k k
|
Unplug the Front Panel LED cable from the connector on the motherboard and plug it into the CN351. To make the LED operate for IDE drives as well, use the extra cable supplied with the A4091 to connect CN308 to the motherboard.
Rear Connector View
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|
|
|
DIP Switch
External SCSI-2 Connector |
| _________________
|
| ON |
| 1
25 |
| | 1 2 3 4 5 6
7 8 | {}:::::::::::::::::::::::::{} |
| OFF |_________________|
26
50 |
|
|
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DIP Switch Settings, defaults are all OFF
SCSI Address of Card
0 1 2 3 4 5 6 7
SW1 ON OFF
ON OFF ON OFF
ON OFF
SW2 ON ON
OFF OFF ON ON
OFF OFF
SW3 ON ON
ON ON OFF OFF
OFF OFF
SCSI Fast Bus
SW4 OFF indicates that the
SCSI Fast Bus feature is enabled.
Set
this switch to ON if none of your SCSI devices
support
SCSI Fast Bus.
Short/Long Spinup
SW5 OFF indicates that your
system uses the standard spinup
(booting)
time. Set this switch to ON to request a longer
booting
period. If one of your SCSI devices has a long
power-on
cycle, the Amiga may not recognise it during the
standard
booting period.
Synchronous Mode
SW6 OFF indicates that the
synchronous mode feature is enabled.
Set
this switch to ON to disable synchronous mode. Synchronous
mode
does not require acknowledgement for every byte transmitted,
which
can mean improved response time with most SCSI devices.
External SCSI Termination
SW7 OFF indicates that you
do not have any external devices.
This
activates the terminator on the board since this is
one
end of the SCSI bus. Set this switch to ON when you
install
an external device. This disables the termination
on
the board since it is now in the middle of the SCSI bus
(not
at the end).
Logical Unit (LUN) Enable
SW8 OFF indicates that unit
0 is the only unit recognized. Set
this
switch to on to enable the system to recognize 1-6 as
LUNs.
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