PDP-11 Controller needed to use a couple of RX33 drive

Pete Turnbull pete at dunnington.plus.com
Thu Jun 18 02:05:13 CDT 2009


On 17/06/2009 16:34, Johnny Billquist wrote:

> It's actually worse. The write enable signal apparently always gets to 
> both drives no matter what else you are doing. So when you write to one 
> drive, the other will also start writing, even if the head is moving 
> right at that time. I've had to recover an RD53 which was destroyed that 
> way. (Salvage as much data as I could, and then reformat the drive.)

That won't happen unless both drives are also selected.  Having the 
write enable signal go to both drives at the same time is normal in 
ST412 systems, and indeed all the signals go to all the drives at the 
same time in such systems.

> The funny thing is that DEC actually do write in the documentation that 
> it is not permissible to have two hard drives in a BA23, but that note 
> is not so easy to find, and if you don't have the documentation, it even 
> easier to assume that you can, since you do have connectors for two drives.

The DEC information actually says that it's because of the power 
requirements.

> I believe it's a hardware "bug", which can't be fixed without cutting 
> wires, and adding new ones. But maybe someone knows better here?

Mine works, and I've not cut any wires.

-- 
Pete						Peter Turnbull
						Network Manager
						University of York



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