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Mulitple 3.5 fdd

Started by tjohnson, 13:16, 30 April 17

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tjohnson

Hi all. Since my internal drive is dead for now i thought about using a couple of 3.5 drives i have lying around here.  They are slightly odd as they are 26 pin 720 citizen U0DC drives from an old machine  but anyway my question is can i connect an a and b drive off the external connector or does one have to use the internal ribbon connector.  Obviously ill need to make sure the pin out aligns so will need to build a small interface board and they are also 5v drives.  I don't want to mood the case so the easiest option is having them external.  Cheers Trevor

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pelrun

Yes, the floppy bus is shared with every drive in the system, including the internal one - otherwise the ABBA switch mod wouldn't work.

tjohnson

I'm not so sure, had a look at the circuit diagram and can see NDSEL0 goes to the internal floppy and NDSEL1 so not entirely straightforward I think as the edge connector doesn't carry both.  Having done more searching I can see the  "ABBA" switch is used to swap which drive is A and B.  Having said that if there are spare pins on the edge connector I imagine it would be possible too jumper over Drive 0 to the edge connector and connect it through, looks like there are 4 spare 21, 29,31 and 33.  I'm going to have to make some sort of custom adaptor for these drives anyway.  Anyway I could be making this all up as I'm no expert on these things.

pelrun

The drive select lines choose which drive to enable, because every drive sees the same signal lines. You either reconfigure the drives (if possible) so that one responds to DS0 and the other to DS1, or if they both are locked to DS1 you swap the two wires going to one of the drives so it sees DS0 as DS1 and vice versa. (this is why old PC floppy cables have a twist in them before one connector.)


Every other line is identical.

tjohnson


What I would like is drive a and b off the edge connector without having to switch or swap cables around etc such that they respond appropriately.  When I posted I hadn't look at the circuit diagram, now I have I can see the drive select line 1 goes to the edge connector and line 0 goes internal.  The ABBA switch mod looks like it switches the signals around so DS0 arrives on the edge and DS1 internal.  If I want to have both connected on the edge connector then I need to get the DS0 signal on there in parallel and then wire it accordingly to the appropriate pin on the drive, so there is no switching or swapping of cables etc.  Could be a nice little project, I'm thinking edge socket onto a PCB then 2 headers on the PCB one for each drive to plug into.  Again, I'm no expert in this so I could be talking out my.....and it will never work.

CraigsBar

It's possible yes. But quite how I am not sure. When @Bryce did my 464+ upgrade he brought both A and B out on the centronics connector so I can have drives work exactly as they are jumpered.

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pelrun

Ah, ok. All you need to do then is bring the internal DS0 signal out to the DS0 pin (21) on the edge connector with a wire jumper. (sorry, it looks like I confused you a bit by mentioning the ABBA switch.)


A PCB is probably a little overkill; I think it'd be much easier just to make a cable with 3 connectors on it like the old PC floppy/hard drive cables. Ignore me I forgot they've got an unusual pinout.

Bryce

Quote from: CraigsBar on 16:17, 30 April 17
It's possible yes. But quite how I am not sure. When @Bryce did my 464+ upgrade he brought both A and B out on the centronics connector so I can have drives work exactly as they are jumpered.

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Yes, that's possible on the CPC+ machines because there was a spare pin on the port, but not on a Classic CPC.

Bryce.

tjohnson


Hi Bryce, the circuit diagram indicates there are some spare pins on the external edge connector I could use, or am I wrong? 


So not much progress to report, I thought I'd test power to the drives,  I thought the pinout would be a standard slimline 26 pin fdd pinout which I've searched and checked but having some doubts.  I hooked up 5v to pins 1, 3, 5 and the then hooked up the ground pins.  No indication on the drive although the only led appears to be a read led.  Anyway, when I removed 5v from pin 5 the motor started to spin, which seems odd and I thought maybe this is actually the motor enable pin however the standard pin out would put that at pin 10.   I'm not feeling too confident about hooking the drive up to the CPC incase I send voltage into the machine.

rpalmer

tjohnson,

Floppy drive signal are normally active low meaning if they are grounded the drive will act upon them.
Some very old non-standard 5.25 and 8 inch drives had the signal active high

rpalmer

tjohnson


rpalmer,
Here was what I was thinking for the pinout to the Amstrad - labelled using the references in the service manual.  Still worried about the fact that the motor came on when disconnecting pin 5 from 5v.  As you say the motor may operate when low so this could indicate its the motor enable pin which would mean it had a very odd pinout and will be difficult for me to use it.  I can't find a datasheet for the drive.  The PCB can't come out without dismantling the whole drive which I really don't want to do.
Cheers Trevor

pelrun


Quote from: Bryce on 11:17, 01 May 17
Yes, that's possible on the CPC+ machines because there was a spare pin on the port, but not on a Classic CPC.


Really? The pinouts I have state that DS0 is on pin 21 (as it should be, since it's a standard shugart pinout), but it's n/c.


Quote from: tjohnson on 23:56, 01 May 17Still worried about the fact that the motor came on when disconnecting pin 5 from 5v.  As you say the motor may operate when low so this could indicate its the motor enable pin which would mean it had a very odd pinout and will be difficult for me to use it.




I strongly doubt it's got inverted signalling (especially since it's been used in the Amiga, which is also shugart compatible.) It's more likely that that particular 5v pin is either independently powering the logic, or it's an extra signal of some sort that's expected to be tied high for normal usage. Just make sure all three pins are connected to 5v and you should be fine.


Also, everything that's not power is just signal lines; even if they're hooked up wrong or inverted you won't damage anything - it just won't work.


Audronic

#12
@tjohnson


I found this pinout for  a Citizen X1DE-0OR it MAY be of some help ?




http://info-coach.fr/atari/hardware/_fd-hard/citizen-x1de00a.pdf

Ray
Procrastinators Unite,
If it Ain't Broke PLEASE Don't Fix it.
I keep telling you I am Not Pedantic.
As I Live " Down Under " I Take my Gravity Tablets and Wear my Magnetic Boots to Keep me from Falling off.

Bryce

Quote from: pelrun on 00:56, 02 May 17

Really? The pinouts I have state that DS0 is on pin 21 (as it should be, since it's a standard shugart pinout), but it's n/c.



Are you confusing NDSEL (direction select) with NDSEL0 and NDSEL1? The Drive Select pins are DS0 (pin 4) and DS1 (pin 6 but not connected) on the internal (26way) connector in the CPC+ and on the rear port theses are DSO (pin 9 but not connected) and DS1 (pin 11).
To modify Craigs computer I just connected a wire between the internal header (pin 4) and the rear connector (pin 9) so that both DS0 and DS1 go to the external port. Otherwise only Drive B: would be available externally.

Bryce.

pelrun

#14
Remember the pin numbering on the original 6128 external drive connector is reversed in Amstrad's diagrams. DS0 on that is pin 21.


http://www.cpcwiki.eu/index.php/Connector:2nd_disc_drive_(CPC664,_CPC6128,_CPC6128%2B)

Audronic

@pelrun


Sorry the link does not work.
But in the wiki do a search for " connector " and it is there.


Ray
Procrastinators Unite,
If it Ain't Broke PLEASE Don't Fix it.
I keep telling you I am Not Pedantic.
As I Live " Down Under " I Take my Gravity Tablets and Wear my Magnetic Boots to Keep me from Falling off.

Bryce

Quote from: pelrun on 17:40, 02 May 17
Remember the pin numbering on the original 6128 external drive connector is reversed in Amstrad's diagrams. DS0 on that is pin 21.


http://www.cpcwiki.eu/index.php/Connector:2nd_disc_drive_(CPC664,_CPC6128,_CPC6128%2B)

Ah, you're right. So it is possible on the classic CPC, you'd just need to connect the DS0 from the internal drive to this pin to get A: and B: drives externally.

Bryce.

tjohnson

Thanks chaps,  i may not need to now as the original drive is now close to working fully, but would still like to rig up a 3.5" for data transfer.  Will update this when i get more time to spend on it


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