The Oktagon 2008S is a combination SCSI-2 (but not Fast SCSI-2) and 16-bit RAM board, much like the A2091. However, the Oktagon in combination with the A4000 does not have the extremely slow transfers of the A2091 (see Slow A2091 Problems because the Oktagon does not use DMA; it uses interrupt-driven PIO.
The Oktagon uses 1Mx4 ZIP chips, either static column or page mode, to provide 16-bit RAM. An IDE version of the board is also available (2008AT).
Oktagon ROM versions of less than 6.5 may have problems with removable media devices. The recommended (current) version is 6.8. To see the current ROM version number, press F1 during powerup, or use C:Version on oktagon.device.
Problems have been reported using the Oktagon with 68060 accelerator boards. The Oktagon ROM uses a MOVEP operation, which is an illegal instruction on the 68060. An A4000 with a 68060 board and the Oktagon will refuse to boot because of this problem. Revisions 6.10 and 6.12 of the Oktagon ROM correct this problem.
There is a "Multi Initiator" option in the Oktagon preferences program. Enabling this will prevent the board from sending resets to other SCSI devices, which may help when sharing peripherals between multiple computers. There is also an option to disable parity checking, which may be necessary for using older SCSI devices that don't support parity.
Board Layout
_________________________________________________________________
| Jumper
|___
| : ::::::
:: SCSI
|
|LED 123456
:: Connector
|
|
::
|#
| ::::::: 63,83
::
|# External
| ::::::: 23,43
::
|# SCSI
| ::::::: 62,82
::
|# Port
| ::::::: 22,42
::
|# (DB25)
| ::::::: 61,81
::
|#
| ::::::: 21,41
::
|
| ::::::: 60,80
.
|
| ::::::: 20,40
: Power
|
|_________________________________________________________________|
|||||||||||||||||||||||||||
|
Jumpers
1: SCSI Enable/Disable (Open: SCSI
enabled, Closed: SCSI disabled)
(On the IDE version, this
enables or disables the IDE port.)
2: Memory Enable/Disable (Open: Memory enabled,
Closed: Memory disabled)
3: MS0 (see below)
4: MS1 (see below)
5: Test Mem
(Open: Autoconfig, Closed: Don't autoconfig)
6: Terminator Power
(Open: None, Closed: Supply +5V SCSI term power)
Memory Size Configuration
Memory Size MS0 MS1
Chips Added To Sockets
----------- ----- ------ ----------------------
2M Open Open 20,21,22,23
4M Closed Open 40,41,42,43
6M Open Closed 60,61,62,63
8M
Closed Closed 80,81,82,83