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Started by St-BeidE(DE/GB), 19:08, 26 November 23

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Background 1:
The german manual for the CPC6128 has a big fault.
It shows the pinout of the international CPC with edge connectors.  Also the numbering between CPC german and CPC Plus computers changed... Amstrad/Schneider
did their best to confuse me...
Background 2:
Its more than 10, maybe 15 years ago, that I had my CPC System up and running. I remember, I had a special method of ABBA "switch", developed by @Nilquader of spring. He may rest in peace.You cannot view this attachment.

I also had a Symbiface II, packed together with that "Drive B" into a housing. In front of that housing, there were all those switches needed to operate Symbiface AND Diskdrive.

To make that possible without an additional wire, 
I used one of the (hopefully) unused pins of the
Drive connector.
You cannot view this attachment.

---‐  -----   -----  -----   -----   -----   -----   -----   -----
Well, I do not own the Symbiface II any longer.
Together with the box, the switch and its connection
also disappeared. :doh:

I DO own the successor RSF3 now and am trying
to reconstruct the drive switch...

PLEASE  help  :-[

May somebody tell me, what Pin I used?
I ' m not interested in fighting with numbers.
They don't tell me the use of the pins. So that
won't help...



On this site there are the different pinouts including the 6128 centronics one ->

Oh and here is the original PDF of your Switch ->


Quote from: SkulleateR on 19:44, 26 November 23On this site there are the different pinouts including the 6128 centronics one ->
I'm afraid it even confuses me more.



The Schneider CPC Systembuch (Sybex) explains the situation and has an overview of the pin numbers compared to the edge connector. Maybe this clarifies it.


    you didn't use an unused pin. That's pin 3. It's function is "Side Select", ie: That's the pin that decides whether the drive should read side A or B of the disk. The ABBA mod is setting it high or low to select the side.



Quote from: Bryce on 23:08, 26 November 23Hi,
    you didn't use an unused pin. That's pin 3. It's function is "Side Select", ie: That's the pin that decides whether the drive should read side A or B of the disk. The ABBA mod is setting it high or low to select the side.

Sorry, but I have doubts.
Thats what I mean. Schneider changed counting the pins without a good reason. It is Centronics Pin 3, but I
think it has nothing to do with the pinout numbering
of the floppy port.
I could swear, it worked those days.
The pin number must be 33 or 34 ?
So, wether it is not connected, or it is assumed
to be GND -
If the IC has a "pullup resistor" on input pin, it
would be enough to force input to ground by
What makes it even more difficult is, the small PCB below the 74LS00... traces are between PCB and IC, hard to see.
:picard: the more I think about it, the more confused I am.

I have to measure it tomorrow, or remove the whole
Amstrad PCB ... at least - n.c. means Not Connected.
With my glasses on, I should see the absense of traces.


Quote from: eto on 21:58, 26 November 23.... Maybe this clarifies it...
;) yes ! It clarifies the confusion.

QuoteDas hat die Hardware-Designer bei Amstrad möglicherweise bewogen, auch die Pin-Nummerierung auf den Kopf zu stellen. Während beim Drucker- und Systembus-Anschluss der Kontakt rechts oben (Sicht von hinten) jeweils die Nummer '1' erhielt, ist es hier der Kontakt links unten.
Da beim CPC 6128 die Floppybuchse aber in der selben Lage wie der Druckeranschluss eingebaut ist, kann die Nummerierung hier nicht mehr übereinstimmen. Erschwerend kommt noch hinzu, dass beim Platinenstecker die Kontakte wieder alternierend durchnummeriert sind (oben alle geraden, unten alle ungeraden Anschlussnummern), während bei der (Centronics-) Buchse für das Floppylaufwerk die Nummerierung oben von 1 bis 18 und unten von 19 bis 36 geht.
Hier stimmt also nichts!
In English:
QuoteThis may have prompted the hardware designers at Amstrad to turn the pin numbering upside down. While the contact at the top right (viewed from behind) of the printer and system bus connection was given the number '1', here it is the contact at the bottom left.

However, as the floppy socket on the CPC 6128 is installed in the same position as the printer connection, the numbering can no longer match here. To make matters worse, the contacts on the PCB connector are numbered alternately (all even numbers at the top, all odd numbers at the bottom), whereas the (Centronics) socket for the floppy drive is numbered from 1 to 18 at the top and from 19 to 36 at the bottom.

So nothing is correct here!
Please expand for maximum fun...

But, Yes. I'll verify this tomorrow with a Multimeter
and an optical inspection. At least we know, witch
side is witch, then.



Quote from: St-BeidE(DE/GB) on 19:08, 26 November 23The german manual for the CPC6128 has a big fault.

Mistakes can happen. What annoyed me back in time was, that Schneider never made a correction to the manual and even when Amstrad distributed Schneider CPC in Germany they made a new manual in 1988 - but kept this mistake in it.


I got the solution.

You cannot view this attachment.
As you can see, this is the undersite of my CPC 6128.
Don´t let the white PCB print fool you. The numbers
printed at the board are WRONG !!!
This is easily proved by controlling the GND Line.
All Pins with an EVEN numbering must be GND.
So the printed numbering it is not possible.

I made a drawing to show the correct pinout

You cannot view this attachment.

While I could NOT prove pin 33 and 35 to be NOT connected,
I savely proved, 1 and 3 ARE connected.
That in mind, the numbering must be as followed:

Just to visualize the correct assumption of the
GND line, have a look at the side view of the
centronics connector and its wiring.

You cannot view this attachment.

So, what I probably did, was, to use the pin 34 as a
signal line for switching. If an unmodified floppy is
connected, it does not matter. GND will be applied
to pin 34 and nothing happens.
If, however, a modified floppy with a (on/on) switch
is connected - and the switch applies 5V to the line,
the IC changes adressing A / B to B / A.


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