[Coco] Tandy Hard Disk Controller

[Gene Heskett]

On Friday 03 March 2006 19:27, Bruce W. Calkins wrote:
>The Disto Hard drive adapter is SASI.  (I don't know about the
> 4-in-1.)  It runs a SCSI to MFM board on my CoCo Hard Drive system. 
> If I understand correctly, the protocols are backwards compatible. 
> Which is one reason I've not given up on "my" Tandy hard drive
> "controller" yet.

The 4n1 is scsi, but missing a few signals in the middle of the cable.  
It works by splitting the 34 pin cable in the middle and crimping the 
resultant 17 wire pairs into the outside 17 at each end of the 50 pin 
connector.  Or is that in fact SASI also?  No other controller was/is 
needed, it talks to the scsi-II drive just fine that way, and at the 
same speed for a megaread as you can do from a ramdisk, about 11 
seconds on a 6309 in 6309 mode.  In other words, the drive is waiting 
several eons in computer time for the coco, read or write since the 
drive is usualy able to move at least 10Mb a second.  Memory is getting 
hazy but I believe my old Maxtor 7120s was rated at 20Mb/second.  Very 
early scsi-1 drives were 5Mb/second IIRC.

One thing the 4n1 users might run into is that one of the missing 
connections in the middle of the cable is term power, so the drives 
MUST be jumpered to furnish it themslves.

>Bruce W.
>
>> And I'm told it wasn't even scsi, but sasi,

-- 
Cheers, Gene
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