The ZX81 FDC FLOPPY CONTROLLER [Kicad]

[XavSnap]

Hi all,

My Next project will be a rebuiled from the M. KNISPEL FDC Floppy Controller. (from 1987-1990)

Have a look to the PDF include in this thread : https://www.sinclairzxworld.com/viewtop ... f=7&t=2571

The PCB can be printed as is with the original PCB, but the scan of the both face don't properly match together.

But, this first release give a first look to the original project.

This project is unused now, the SD loader is cheaper & more reliable... (we had to pug a floppy disk emulator like a Gotech)

But it't a new challenge to create a clean PCB and integrate multi-floppy feature.

Have fun, and let me know regards new vintage ideas...

Thanks to the german ZX-Team for diagrams and there work (KLS und Franzis-Verlag...)

Diagram:

FDC_ZX81_Controller.pdf

(535.9 KiB) Downloaded 64 times

Kicad PBC & Diagram: (no gerber due to the poor quality)

FDC_ZX81_FDController_Original.zip

(2.16 MiB) Downloaded 62 times

[XavSnap]

Hi,

Step 1: Import a double side PCB, copper/component sides.
Most of the time this PCB is functional as is, no schematic is needed.
It's done.

But we had to check the PCB to suite to a proper wirring diagram.
We assume the PCB is working, and the schematic was drawn to build it (no updated!).

We assume last minute changes may not have been taken into account in the diagram.

Step 2: Check the shematic diagram.
We had to change the layer and swap both sides on a working layer, and redraw all tracks over graphics tracks.
If the shematic diagram don't match, we had to change it if the component's pins are wrong.
It's done.

Note : The imported graphic layer can't be exploded, and can't be use as a copper track/layer to shortcut the pins and be compared vs the wiring diagram net-list. We had to link them using the copper track tool.

FDC_ZX81_Controller.pdf

(606.21 KiB) Downloaded 59 times

Kicad files:

FDC_ZX81_FDController_CHECK.zip

(1.08 MiB) Downloaded 59 times

Step 3: Time to make a new PCB using this retroengineering.

[XavSnap]

Hi,

"38" Vs "251" vias !

It was a tricky puzzle... But, it's done.

Shematic:

FDC_ZX81_Controller.pdf

(656.18 KiB) Downloaded 61 times

But, on the drive socket pcb, i don't understand why you able to select the drive !

[XavSnap]

Wath is the "POKE-Erweiterurg" ?

[Paul]

It's the poke8 extension that uses a latch and replaces jumper for configuration

[XavSnap]

Thanks Paul,
I had to add a POKE decoder on the mother card.
I had to retrieve the drive select memory offset in the zxDOS routines...
Add a latch to select the right dive destination.
Exemple:POKE 0,0 = <drive 0 ...
A jumper can select the master disk drive, but the multi-drive can't be use for now.
I had to update the main FDC controller card.

[Paul]

Pay attention. You can't use poke 0.
Addresses 0 to 5 are written to by the calculator.
Poke 8 ist First easily addressable number.

[XavSnap]

Hi Paul,



Not the easy way to select a drive.
But, if this "POKE 8,"... is used to it.

The easy way is to POKE something in the EPROM (CAS0 beatween $2000-$27FF) and drive it by a /WR...
I wonder if i add to put a daughter PCB on the original one...
One disk is probably enough ?

POKE8 addon:

[1024MAK]

Two 74HCT688 8-bit magnitude comparator chips can be used for the address decoding. Each chip has two groups of eight inputs. It’s single output is active (logic low as it’s inverted) when the two groups of inputs match. So for each chip, connect one group of inputs to eight address lines and the other group of eight to fixed logic levels (0V/GND or +5V/VCC) as required to set the wanted address.

Each chip has an enable input as well, this can be used for a control signal such as /MREQ or /WR.

I’ll do a schematic later.

Mark

[XavSnap]

HI,
Thanks Mark, i have ever used this ship, just used this kind of chip to use the spares...
But, if i use an add-on pcb, it will be easy to use two 688 [edit:74LS388 (688 don't give a global output) was 688, not 388 ! Sorry. You're right.]. It will be a better choice.

I can't fugure out the POKE8 card, but pickup pins on the controller card is "nutzlos".
We only had to redirect /motor_on... ?