Date   : Sun, 19 Dec 1999 13:58:03 GMT
From   : theomarkettos@... (Theo Markettos)
Subject: Re: ZIP drives for BBCs

On Fri, 17 Dec 1999 12:58:39 +0000, Gareth.Boden@... said:

> Certainly SuperDisk drives are capable of being used over the standard 2 or
> whatever-it-is inputs of 'unidirectional' parallel ports. I presume the
> Parallel IDE or SCSI chipsets are pretty standard in this respect.

Unidirectional PC parallel ports have a few more inputs than just 2 (I count
5 - ERROR, PE, SLCT, BUSY and ACK), which means you can squeeze nybble
transfers through them.  With a Beeb only having one parallel port input
line, you might have some trouble.  However, you could amalgamate the
parallel and user ports to give more than enough lines to do it.

A 1MHz bus IDE interface for a Beeb would be quite simple - all it needs to
do is choose two block of 8 addresses, and feed an enable signal for each of
those blocks to the drive.  It's complicated a little by the 1MHz bus only
being 8 bits wide, but a couple of latches can be used to transfer the IDE
bus 16 bit words in two 8 bit chunks.  I've not looked at the timing aspects,
but I think modern drives should react sensibly when accessed at 1MHz -
AFAIK there's no timeout specified in the ATA spec at all, so driving
software can be as slow as it likes.

IDE hard drives would be fairly straightforward to write software for - I
think HDFS could take care of the filing system side of it.  IDE Zip drives
use ATAPI (IIRC), which makes the software a little bit complicated, and
similarly with SuperDisk (which also wouldn't be able to read Beeb floppies).
It's still reasonably doable, just a bit more complicated...

Theo

-- 
Theo Markettos       atm26@...      
Liphook              theomarkettos@...          
Hampshire            
UK                   http://www-stu.cai.cam.ac.uk/~atm26/