cable DDI-1 for CPC 6128

[willow3411]

Hello everyone,
So here I am going to try to be clear in my explanations.
I have a Schneider DDI-1 (external reader) with its Amsdos interface for my CPC 464. Everything works perfectly.
I would like to make a cable that directly connects my DDI-1 to my CPC 6128 (EDGE port).
Just by replacing the AMSDOS interface.
of course I would like to keep my internal 3" drive in A and the external one in B
I have the 34p cable, the 34p female connector and the EDGE connector.
The problem is that I don't know the exact pinout. I read a little bit of everything.
If anyone has a diagram that would be great.
Thanks for reading me.
Willow3411

[Bryce]

https://www.cpcwiki.eu/index.php/File:Floppy_Cable.png

Bryce.

[willow3411]

https://www.cpcwiki.eu/index.php/File:Floppy_Cable.png

Bryce.

Hi Bryce!
Thank you for the link
I already had it.
so it's wire to wire wiring?
Thanks

[robcfg]

Isn't the DDI-1 wired to supply 5v on the floppy cable?

Could that damage the CPC?

[McArti0]

https://www.cpcwiki.eu/index.php/DIY:Floppy_Drives

[willow3411]

https://www.cpcwiki.eu/index.php/DIY:Floppy_Drives

Thank you, I saw this page but I don't understand the wiring.....
is it wire to wire?
The goal is not to disassemble my DDI-1 but just to change the cable.
I saw on a forum that it was necessary to cut tracks on the tablecloth...

willow3411

[McArti0]

https://www.cpcwiki.eu/index.php/DIY:Floppy_Drives#Pinning_translation_between_different_connectors_.28CPC-PL-9.2C_Centronics_36pin.2C_Floppy_connector_34pin.29

[eto]

Just to avoid confusion: The DDI-1 is the floppy controller for the 464 with AMSDOS, the disk drive alone is the FD-1.

Generally speaking all you need is a 1:1 connection from edge connector to IDC floppy connector. An old PC floppy cable that has both connector types for 3.5" and 5.25" would perfectly fit (as long as no pins are flipped).

The FD-1 injects 5V into some of the wires, that are not required on the 34p cable. The DDI-1 is using that power for its electronics. On the CPC - at least according to the schematics, these pins are not connected. So (in theory) it should be save to simply connect the FD1 with a normal cable to the CPC.

HOWEVER:
1) I have never tried myself and verified it.
2) Also it's easy to attach the cable upside down as neither the FD-1 connector nor the edge connector on the CPC prevent that - or you can just mix up directions when crimping the cable. Cutting the tracks won't help if you connect the cable upside down. Not sure if the 5V injected by the drive can harm the computer but To be honest I would prefer not to try it out and just disconnect the 5V injection inside the FD1.

[willow3411]

https://www.cpcwiki.eu/index.php/DIY:Floppy_Drives#Pinning_translation_between_different_connectors_.28CPC-PL-9.2C_Centronics_36pin.2C_Floppy_connector_34pin.29

Thanks a lot !

donc c'est bien un cable point à point si je comprends bien .

[willow3411]

Just to avoid confusion: The DDI-1 is the floppy controller for the 464 with AMSDOS, the disk drive alone is the FD-1.

Generally speaking all you need is a 1:1 connection from edge connector to IDC floppy connector. An old PC floppy cable that has both connector types for 3.5" and 5.25" would perfectly fit (as long as no pins are flipped).

The FD-1 injects 5V into some of the wires, that are not required on the 34p cable. The DDI-1 is using that power for its electronics. On the CPC - at least according to the schematics, these pins are not connected. So (in theory) it should be save to simply connect the FD1 with a normal cable to the CPC.

HOWEVER:
1) I have never tried myself and verified it.
2) Also it's easy to attach the cable upside down as neither the FD-1 connector nor the edge connector on the CPC prevent that - or you can just mix up directions when crimping the cable. Cutting the tracks won't help if you connect the cable upside down. Not sure if the 5V injected by the drive can harm the computer but To be honest I would prefer not to try it out and just disconnect the 5V injection inside the FD1.

Hi Eto
ah great explanations
I understood everything !
Thanks a lot
tomorrow I make the Edge tablecloth ---> IDC 34p 1:1
beautiful evening
and thank you all!!
I will report back to

[Rabs]

Isn't the DDI-1 wired to supply 5v on the floppy cable?

Could that damage the CPC?

I read this also somewhere, not sure if it is correct but as I am only using with a CPC 6128, I disconnected the internal 5V supply just in case I initially got the cable upside down. Guess I can reconnect now it is working.

You cannot view this attachment.

[willow3411]

Hi all !
So here is my return
A 1:1 tablecloth is what you need.
No need to unplug the 5v in the FD1
we connect as in my photo (I printed stickers so as not to get the wrong direction), and it is recognized on disk B
Thank you Eto and all the others for your always valuable information!!!

Thanks @eto @Rabs @Bryce 

Willow3411

[SerErris]

The original design for the B drive on a 6128 was to use the normal FD-1 with a normal cable. So the 6128 is indeed prepared for the 5V lines. Also those lines are anyhow signal lines with active low. So the only problem would be if the CPC would pull them down. But as that never happens it is not a problem that they are high. There is no such thing like power injection. It is power will get pulled. And as this is correct voltage level even if it would be connected to something that is internal 5V it would not damage anything.

So from single point of view those lines are unused in the CPC and only used for power supply on DDI-1.

[Bryce]

The original design for the B drive on a 6128 was to use the normal FD-1 with a normal cable. So the 6128 is indeed prepared for the 5V lines. Also those lines are anyhow signal lines with active low. So the only problem would be if the CPC would pull them down. But as that never happens it is not a problem that they are high. There is no such thing like power injection. It is power will get pulled. And as this is correct voltage level even if it would be connected to something that is internal 5V it would not damage anything.

So from single point of view those lines are unused in the CPC and only used for power supply on DDI-1.

Not quite correct. The lines used for the 5V supply were otherwise GND lines. They aren't connected on the 6128 side to avoid a short circuit and on the DDI-1 the connector nearest the expansion has those pins removed from the connector to avoid damage if you were to add a second drive.

Bryce.

[SerErris]

Checked it again in the service manual.

Odd PIN numbers are all signals and even are all GND.

In normal shugart or PC connectors those pins would be 2-34

SHGT or PC
2 /DCD or /Density
4 /INUSE or NC
6 /DS3 or NC

[Bryce]

Yup, because Amstrad messed up the pin numbering too!

Bryce.

[SerErris]

That is what I said:

Amstrad PIN 1-33 are signal pins, where shugart it is the even pins (2-34).

So we are talking about the same signal pins, that are never GND. At best they are NC.

Amstrad did just turned the connector arround, so that even will be odd and also that PIN 34 will become PIN 1 (READY)

Following that The Amstrad PINs 29,31 and 33 carrying +5V from diskdrive to power the controller (Amstrad Schematic) and that will convert to PINs, 2,4 and 6 on Shugart BUS.

As described above, all of those are signal pins and not connected to GND on shugart bus. Pin 2 and 4 are drive to interface pins, so there should be a pullup on the interface side (or on the drive side), but there is nothing driving the line from the interface to low and interface side should be on high impedance, so it should not be an issue. 
Pin6 however could be a driving pin with driver select 4. However on the CPC infrastructure, the DDI-1 does not use this line for anything (as well as DS3). 

In the Schematics of the 6128 Service manual, it looks like the cable would be connected to +5V...
You cannot view this attachment.

However looking at the board, they are really not connected.
You cannot view this attachment.

Anyhow, regardless if you connect it with cut lines or not, it will not harm the CPC (which we agree on :-) ).

[Rabs]

Would I be ok if I accidently got the cable upside down?

[SerErris]

If you get the cables upside down, all signal lines from the drive will get connected to GND and all signal lines from Interface will get connected to GND as well.

However it looks like that the architects of the CPC again thought about that issue and developed protection

Lets analyse the technology  if you connect one end wrong way.

Lets see how that would look on CPC end:

All output signals from 765 Controller are connected to 74LS38  "2-INPUT POSITIVE-NAND BUFFERS WITH OPEN-COLLECTOR OUTPUTS". Those open collectors mean, that they can only pull a line down, but cannot send out +5V on their own. It requires that the line is getting pulled up via a pullup resistor against +5V power source. Those pull-up resistors are located in the drive itself. That does two things: First the current possible to flow from +5V to this input is limited by this pullup resistor. Second this open-collector output will get connected to GND if you put the cable upside down, so it is anyhow and allways GND and no current will flow at all, so no damage to that side.

Input signals to 765 are connected the other way around via a Schmidt-trigger buffer chip, that also requires a pull-up resistor. Those input-pull ups are located in the interface of the CPC and the only current flowing is from +5V from CPC to GND in the drive via the pull-up resistor. That means the input is protected, it will never get any high current flowing in. The maximum current in this particular case at +5V with 680Ohm pull-up is 7.5mA .. That is the total impact per line to the power supply of the CPC. So for any input signal there is no harm to the CPC.

Now lets look at the drive end:
Here again all Output lines are requiring pull-ups and connecting the outputs directly to GND will not harm them in any way. There is simply no current going through it at any time.

Regarding the input lines. They are all connected again to pullups (as described above). In the drive case it is 1k resistors so the current is even lower at 5mA. This is very low and it will get directly go to gnd, and that is the maximum current that is drawn per line from the power supply. As this is a 1A power supply it also will have no problems with it.

The last lines that are potentially dangerous are our beloved +5V power supply lines for DDI-1.
On the CPC side of things, there is no damage, as the lines are directly connected to GND and that does not harm the CPC at all.

However it is potentially dangerous on the drive side as this can grill the voltage regulator. It will have no effect on the drive logic (the drive itself), but it may damage the power supply of the drive. Also there are two independent +5V rails inside the power supply. One is for the drive logic itself and one is just for the power supply for the DDI-1. However those 7805s typically come with short protection or overheat protection. If you would short the output to GND it will proabably overheat at some point and then just shut down (no power injected any longer). The worst case would be, you need to replace a burned 7805, which you can then replace with a proper one with short protection nowadays. Maybe that is a good idea anyhow :-)


TLDR:
All in all - nothing will probably happen if you connect the connector upside down and looking at the CPC side of things, actually nothing will happen if you connect it upside down. It could potentially grill the 7805 in the drive, that should power the DDI-1 but that its about it and probably (not sure as my Japanese for the original Sanyo part is not that good :-) ), even that is protected against in the regulator itself.

There is one last thing to mention.
With the correct cable it is impossible to connect it the wrong way. The cable had a particular nose on the drive side and a gap in the connector on CPC side, that prevents it from being connected wrong. So all this topic is a pretty modern issue, where people do not have the original plugs with the coding in the connector to ensure correct connection.

If you look at the connector for the drive on the CPC there is the gap in the pcb, where there is a key in the connector. So you actually would not be able to insert it the wrong way.

Of cause for the Schneider CPC 6128 variants it would even be the connector itself, that will prevent it from getting plugged in the wrong way (Centronics V-Shaped connector)

[Rabs]

Thanks for the info. For some reason I struggle when making ribbon cables and can never trust myself to get them the right way up.

And really I should go to the effort of adding an edge slot key but never do. 

Anyway just in case I forget which way up it should go, I always leave my future self a handy hint. 

You cannot view this attachment.

[SerErris]

Yeah,

another thing would be:

Turn on the drive first (but get the Amstrad CPC power connected). If the drive motor spins, turn it off. Wrong way.