Four drives on a CPC6128 :-)

[TFM]

Imagine: You have four drives on your CPC6128. Your internal 3" drive, an external 5.25" drive and two 3.5" drives (for fast copy between them). Actually all four drives are iirc supported by the Dobbertin D-DOS.

Now... How to realize that?

We know that the FDC has two wires for the selection of the drive. For four drives we would need DS0, 1, 2 and 3 connected properly at the external drive socket.

So imho a "two to four" decoder would do the job?


But i got no idea about hardware. Does anybody here know how to mockt up the CPC for the usage of four drives? Any information would be appreciated.

[Badstarr]

From my adventures building a disk interface for my GX4000 mod, I think that the Floppy Disk Controller IC has space to select between Device 0 and Device 1. If I have interpreted the schematic correctly however, the Device 1 pin is unconnected, and switching between drives is handled by NAND Gates and a Hex Inverter IC so the CPC only ever has DS0 connected in reality. So I guess it would be possible to connect more drives to DS1 via the use of DS1 pin but the a duplicate series of NAND Gates and HEX Inverter would be needed. Of course this depends entirely on how I have read the schematic but maybe Bryce could confirm? 

[Bryce]

Excuse the quality of this schematic, it was hand drawn and then photographed with my phone (I don't have a PC with schematic software with me at the moment). This circuit (simple discrete 2 to 4 decoder) could be used to split the original DS0 and DS1 into DS0 to DS3, but it assumes that it's possible to set both DS0 and DS1 to both 0 or both 1 at the same time, can the CPC do that? Otherwise it won't work.

Bryce.

[MacDeath]

What's the point with 5"1/4 ?

I mean, on my first PC I was quite happy to have a HD5"1/4 to get cheap 1,2Meg disks, but nowadays i'm not quite sure about the interest.


=CPC doesn't support the 1,2meg format I guess.
=Hard to find theses days, even more than 3"1/2...
=come on, need to get rid of any dust at home, like running this in a particle free white room on vacum...



On the other hand, having 4 disc drive is also somewhat too much.

FutureOS does support up to 8 disk drives, funny feature but mostly done because it is possible, but would it be practicle ?
Better to try to have a HDD than that many DiskDrives...

[steve]

One floppy and a ramdisk is probably best, with a CF hard drive ASAP.

[arnoldemu]

Excuse the quality of this schematic, it was hand drawn and then photographed with my phone (I don't have a PC with schematic software with me at the moment). This circuit (simple discrete 2 to 4 decoder) could be used to split the original DS0 and DS1 into DS0 to DS3, but it assumes that it's possible to set both DS0 and DS1 to both 0 or both 1 at the same time, can the CPC do that? Otherwise it won't work.

Bryce.

on the fdc side, ds0 and ds1 are decoded to make 4 drive selects as you have done.

combinations are (ds0, ds1).
0 0,
0 1,
1 0, 
1 1

it's not possible to select more than one drive at the same time.

[Bryce]

With "selecting more than one drive", I actually meant whether DS0, DS1 = 0 0 and 1 1 combintations were possible. which you say is, so 4 drives would be possible

Bryce.

[TFM]

Excuse the quality of this schematic, it was hand drawn and then photographed with my phone (I don't have a PC with schematic software with me at the moment). This circuit (simple discrete 2 to 4 decoder) could be used to split the original DS0 and DS1 into DS0 to DS3, but it assumes that it's possible to set both DS0 and DS1 to both 0 or both 1 at the same time, can the CPC do that? Otherwise it won't work.

Bryce.

Thanks' a lot! That was lightspeed (even the forum was down a while). You are absolutely right. Yes, you can individually set DS1 and DS0 on the FDC (00, 01, 10, 11). Every FDC command has this two bits and can set them both to 0 or 1 (all four combinations).

Now we can try a hardware modification in reality :-)

[Badstarr]

Well I suppose while I'm about it I could do this mod to my GX4000 disk interface as I think I may very well have the components required going spare. I'm not sure I have enough working drives at the moment    What would you say would be a plus point to this setup though? Could we have a sort of "RAID" system setup? Virtual memory maybe? Imagine 4x HxC's ! That would be pretty cool if a little excessive!   

[robcfg]

Oh my gosh!

I've had a revelation!

I've seen a CPC6128 with a 3" drive, a 3.5" one, a 5.25" one and with a magnificent 8" drive!!

Let's call this setup the "Tower of Hanoi" Disk System, hehehe... It really would look funny

[Gryzor]

I agree with MacDeath. 5.25" drives are useless nowadays. Absolutely no need for them - slow, bulky, unreliable media... what less would you want?

Robcfg put it quite nicely actually

[steve]

Now that the age of the 3.5"HD floppy disk is over, I've begun to read claims that they were very unreliable, even stories of the shutter coming off and getting jammed in the drive, can anyone confirm this?

I was going to try and attach two HD drives to a DDI-1 by using the clock for an 8" drive, I am not sure if this would work, but I have now found out that all PC drives are set to "B", so it is not going to be easy.

[Bryce]

Changing a PC drive from B back to A is easy. On most drives there are two small solder bridges labeled DS0 and DS1. Remove the solder from DS1 and bridge DS0 and it's back to being A.

Bryce.

[rpalmer]

you can get all four drives on a standard CPC with a little modification to the floppy chip.

1. The first is to ensure that the floppy chip is socketed otherwise it will need to be rehoused into one.
2. Insert a second socket with the two ds0/ds1 pins bent out so that they are available to attach the circuit as per bryce.
3. Create the circuit on a daughter board (inc. power) with the drive B cable having 4 PC floppy sockets on the cable where each has the drive select connected to one of the decoded ds0/ds1 outputs.  The access point would then have a 2-row pin header inserted so that a normal floppy cable can be inserted.

See attached diagram to see what might be a solution.

rpalmer

[TFM]

I agree with MacDeath. 5.25" drives are useless nowadays. Absolutely no need for them - slow, bulky, unreliable media... what less would you want?

Robcfg put it quite nicely actually

You guys totally miss the point! The point is to have more than one B-drive _WITHOUT_ the need of physically unplugging & replugging them if you want to switch between two of them (if you like 3" and 3.5")

And now some information to the newbies here:    Yes, there are a lot of CPC users who are actually using 5.25" drives.    Now you ask why??? So... think! If you start CPCing in the 80ies, then it was easy to get a cheap 5.25" drive. Now people have a lot of boxes of 5.25" disc. Shall they throw it a away and copy them before to 3.5" - maybe all 700 discs they have? Why should they?

So don't argue about 5.25" here. The point is to have a single external drive _OR_ to have 1-3 external drives. And as I mentioned before: Copy a 80 Trk DS 3.5" with one drive or with two drives - the difference in used time is HUGE, ok? 

[TFM]

Changing a PC drive from B back to A is easy. On most drives there are two small solder bridges labeled DS0 and DS1. Remove the solder from DS1 and bridge DS0 and it's back to being A.

Bryce.

Right, and in the good old days these solder bridges have been JUMPERS!!! Oh, I miss that kind of drives!!!