HD Floppy without Ajax

[+slx]

Is it possible to use a HD floppy drive in double density mode only in an ST that does not have the required (IIRC) Ajax floppy controller for a HD floppy drive. (I have a spare PC HD floppy mechanism which I'd like to use in a Mega ST that does not have HD floppy circuitry but has already been cut out to use regular floppy drive faceplates.)

 

Thanks!

[ParanoidLittleMan]

It is possible, and I used HD floppy drive and disks with my ST back in 1991. But it is matter of luck - depends on will WD1772 chip work reliable at double clock rate.

And of course, you need circuit, what gives 16 MHz to FDC chip when it is active, HD sensing line attached ...  And some steprate fix SW .

[+slx]

On 8/8/2019 at 5:37 PM, ParanoidLittleMan said:

It is possible, and I used HD floppy drive and disks with my ST back in 1991. But it is matter of luck - depends on will WD1772 chip work reliable at double clock rate.

And of course, you need circuit, what gives 16 MHz to FDC chip when it is active, HD sensing line attached ...  And some steprate fix SW .

Thanks. I was actually looking for something even simpler, using a HD floppy mechanism in DD mode with the stock FDC clocked at the stock speed (i.e. not using HD at all). Would that work or is a DD mechanism required?

[ParanoidLittleMan]

HD drives work in Ataris in DD mode without extra circuit, with regular FDC chip at normal clock rate.

But it will need little work on floppy connector lines. If there are no jumpers on drive to set it as A - and newer ones have no it, they are set as B, then need to swap lines

10 and 12 .

 

[+slx]

Thanks!


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