Soft Sectored RK05

[DaveH]

Some time ago , the cctalk mailing list had some discussion about modifying a 12 sector RK05 pack ( PDP11 ) to make it into a 16 sector for use with the PDP8. This would be very useful for those of us that have few 16 sector but more 12 , I have 1 16 that I dare to put in the drive but about 20 12 sector packs.
However this is a fare exercise and the modified pack would not then be usable as 12 sector and sometime I hope to get my 11/50 running and i might then need them.
So I decided to see if how hard it would be to modify the actual RK05 drive to make it treat a 12 sector as a 16, ie soft sector it. The approach I took was to tap into the M7700, index and sector, pull out the "raw" sector/index" signal, feed this into an external microicontroller, use this to synthesize a 16 sector pulse stream and feed this back to the M7700.

Tonight I successfully formatted a 12 sector pack as 16 sectors, PDP8/m, RK8E, MAINDEC-08-DHRKD-D, rk05J.
WOOPEEE.

Next step is to do a restore of one of David Gesswein's OS8 images and run it for real.
The PIC is the 18F8720 running at 20Mhz, programed in Pascall using the excellent and free mikroPascal compiler, making use of all 5 counter timers !!
When I have done some more testing and tidied it up a bit, the software is a bit rough at present, I will post more details and make it available to others that may be interested.
May even do a utube video if I can remember who I lent my camera to.
Dave H

 

[RSX11M+]

Count me in. Collateral to a lot I have going on. Love to see your solution. Thanks for posting.

 

[MikeS]

Think this could easily be adapted to something like a Vector Graphic system to let you use soft sector diskettes instead of 16 sector HS diskettes (5.25"?

 

[DaveH]

Think this could easily be adapted to something like a Vector Graphic system to let you use soft sector diskettes instead of 16 sector HS diskettes (5.25"?

Hi, sorry for the delay, This may not work so well, the RK05 has a very large platter with a large rotational inertia and once its spun up is not going to change significantly over one revolution, I time one rev and then divide by 16 to get the sector timing, I suspect a diskette drive may not be as constant. Having set that only a test will really tell.
I v done some more testing and the results look promising , one format and several reads, HOWEVER we have hit a snag, the pack im using have not been used for a long time, this is the first time iv had the 12 sectors in a drive, I gave them a good clean but maybe not good enough as I now have a "ticking" sound when the heads load, , NOT good, so im going to have to examine this before i do any more work on the soft sector circuit.
Dave

 

[jackrubin]

Hello - anymore info on this experiment?

 

[TJ_Mossman]

Despite this thread being long dead, I've been wondering about this too as I'd like to get an RK05 running on my PDP-8/e.

I've sent a hub from a 16 sector RK05 pack off to a CNC shop to enquire about the cost of replicating it, or possibly modifying existing 12 sector cartridges by cutting new sector slots and covering up the old ones. If a soft-sectoring approach turns out to be a better option, I'd certainly like to give it a go.