Adaptec ACB 4070 on RamFAST SCSI works!

[jdb8042@blkbox.COM (John D. Baker)]

Some time ago I posted about trouble I had trying to use the
Adaptec ACB 4000 series SCSI-MFM/RLL hard disk controllers with
my RamFAST/SCSI card (Rev C, v3.01a).

I've since managed to get my ACB 4070 SCSI-RLL controller to work
with the RamFAST/SCSI.

The key was to set the ACB4070 to respond to SASI pulse select
device select protocol (as opposed to SCSI level select). There
is a set of jumpers on the 4070 to select which protocol to use.

I figure the whole mess works like this:

 The Adaptec ACB 4000 series boards do not support the IDENTIFY command.
 The RamFAST thus treats the board as a Sider SASI Hard Disk and uses
 the pulse-select SASI device select protocol.  If the ACB 4000 is set
 for SCSI, then the pulse protocol fails to select the controller and
 the RamFAST then beleives it's a Tape Drive, since it knows the device
 is there, but cannot select it.

 When the ACB 4000 is set for SASI, the controller IS selected and the
 RamFAST can work with it just like it would a Sider or Xebec SASI
 hard disk controller.


I also switched the jumper on one of my ACB4010 SCSI-MFM controllers,
but it still could not be recognized by the RamFAST/SCSI.  It would
appear that only the ACB 4000A and ACB4070 can emulate a SASI device
and the ACB4010 cannot.  It's likely that it's a matter of lacking
the complete select hardware as running a 4000A BIOS in the 4010
had no effect.

If anyone gets their hands on an ACB4000A or ACB4070 and would like to
use it with their RamFAST/SCSI, the jumper in question is a series of
three solder pads (square outline) just ahead of the pin-1-end of the
BIOS EPROM.  The middle and "lower" pads are jumpered by a trace on
the circuit side of the board.  cutting this trace and jumpering the
middle and "upper" pads together enables the SASI pulse-select protocol
to be recognized.

BTW, I ran the 4070 with an IMI 5018H MFM hard disk (306 cylinders,
4 heads).  Normally, it would give about 15MB MFM, but under RLL,
it gave a little over 23MB available to ProDOS.  When asked for a
drive type for formatting, I used the Sider D4 setting.  I had no
trouble with the ACB4070 running with the RamFAST (as opposed to
the Xebec 1410 crashing the RF at the end of formatting).


Take care.


John D. Baker ->A TransWarp'802'd Apple //e CardZ180 Z-System nut //
Internet:  jdb8042@tamsun.tamu.edu, @blkbox.com, jdbaker@taronga.com
BBS:  JOHN BAKER on PIC of the Mid-Town [(713) 961-5817] 1:106/31,
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