QL's external MDV port

[tcat]

Hi,

First test PCB populated with components, it is DIY, as I have only common tools that of a hobbyist. No through plated holes, so soldering from both sides is required for some of the pads. There is only one via to be soldered through using a piece of wire.

I was thinking to give edge connectors solder coating, but with my pistol soldering iron this may not yield satisfactory results.

I will try to test with QL, as I have learnt this may put my ULA in danger, is there any specific measurement I can carry out beforehand to minimise this risk?

Many thanks
Tomas

mPort - MDV bus extension board

[Outsoft]

Hi,

First test PCB populated with components, it is DIY, as I have only common tools that of a hobbyist. No through plated holes, so soldering from both sides is required for some of the pads. There is only one via to be soldered through using a piece of wire.

I was thinking to give edge connectors solder coating, but with my pistol soldering iron this may not yield satisfactory result.

I will try to test with QL, as I have learnt this may put my ULA in danger, is there any specific measurement I can carry out beforehand to minimise this risk?

Many thanks
Tomas

mPort-DIY.JPG

Great job!!!!!!

[tcat]

Hi,

I was keeping my hopes possibly too high, in first tests it does not perform as expected.

When connected to the external port, I seem unable to select the drive 3.
With mdv3_ plugged in, mdv2_ keeps spinning on power on.
When I run it without mdv3_ plugged in, dir mdv1,2_ works, dir mdv3_ selects mdv2_ and gives only stats of mdv2_ with empty directory list.

I bleeped all tracks through against wiring diagram beforehand, I measured +5V on L7805 voltage stabiliser.

It seems I must have overlooked something in the mdv select chain logic (comms in/out), also could it be that my transistors have different ECB pinnout to the specs, some missing link I forget to solder?

Being poor at electronics I am grateful for any guidance of Yours.
Many thanks.
Tomas

mPort attached to the QL

[1024MAK]

Can you post some close up pictures of the bottom track side of the board, and of the transistors so we can see what type they are and how they are connected please.

Oh, and did you draw your own schematic diagram, or just copy the details from the QL schematic? If you did your own, post a picture of this as well.

Mark

[tcat]

Hi Mark,

Bottom picture attached, actually test PCB has had two flaws in development, as two small spots in front tracks were etched away, I had to renew them, you can see one next to LED renewed from the bottom, the other next to transistor BC640 renewed from top.

Also attached wiring and PCB track layout.

NEW OBSERVATIONS>>

ZX MD unit connected through mPort, cannot be selected either, but through mdv bus tracks measured seem alright of connector EC1.

ZX MD unit connected right to the QL works!

I measured both transistors in hFE test socket of my multimeter, I can confirm transistor pinouts are alright.

BC547"A", E B C, hFE=180
BC640, B C E, hFE=126

Tomas

[Outsoft]

Hi Mark,

Bottom picture attached, actually test PCB has had two flaws in development, as two small spots in front tracks were etched away, I had to renew them, you can see one next to LED renewed from the bottom, the other next to transistor BC640 renewed from top.

Also attached wiring and PCB track layout.

NEW OBSERVATIONS>>

ZX MD unit connected through mPort, cannot be selected either, but through mdv bus tracks measured seem alright of connector EC1.

ZX MD unit connected right to the QL works!

I measured both transistors in hFE test socket of my multimeter, I can confirm transistor pinouts are alright.

BC547"A", E B C, hFE=180
BC640, B C E, hFE=126

Tomas
mPort - bottom - DIY.JPG
mdport-sch.png
mdport-brd.png

I know very well that :

ZX MD unit connected right to the QL works!



But we can only READ and not so better with a Speccy Unit connected to the QL...write or format...is impossibile...at all.

I think you need to test also that the Speccy MD can work / have the right power with mPort.

This is the key.

The best will be that mPort can support also Speccy MD and can pilot correctly as the QL MD ula do with his internal unit.

[tcat]

Hi,

Another test of mPort.

Connected ZX MD Unit through, please note a little loop link over COMMS IN / COMMS OUT pins to set electrical chain.

ZX Unit can stat as MDV3_, I can dir and load programmes over it.
So it is possibly not totally wrong.

I am now thinking, there must some timing RC constant, that somehow influences the chain logic of drive selection. I read that ULA, apart from operational tape signal amplification and RF modulation, also provides FLIP/FLOP logic to latch selective "1" for the drive.

My understanding so far is, that all MD ULAs connects in a chain, and with their FLIP/FLOPS provide a shift register, and only one can hold "1" at any one time, meaning that particular drive is selected.

Unless I have transistors and other parts badly connected, I may have some wrong values of RC, but which?

Tomas

ZX MD Unit connects and works

[Outsoft]

Hi,

Another test of mPort.

Connected ZX MD Unit through, please note a little loop link over COMMS IN / COMMS OUT pins to set electrical chain.

ZX Unit can stat as MDV3_, I can dir and load programmes over it.
So it is possibly not totally wrong.

I am now thinking, there must some timing RC constant, that somehow influences the chain logic of drive selection. I read that ULA, apart from operational tape signal amplification and RF modulation, also provides FLIP/FLOP logic to latch selective "1" for the drive.

My understanding so far is, that all MD ULAs connects in a chain, and with their FLIP/FLOPS provide a shift register, and only one can hold "1" at any one time, meaning that particular drive is selected.

Unless I have transistors and other parts badly connected, I may have some wrong values of RC, but which?

Tomas
mPort - through ZX - DIY.JPG

Great Idea!!!

So OK for LOADING but NOT for FORMAT and WRITE, right Tomas?

[tcat]

Hi,

I just wish to report that mPort works!

The problem was with the ZX ribbon cable, that I found out converts signals on EC1 port, it seems that it swaps upper signals for lower.

At one end>>

8A 7A 6A 5A 4A | 2A 1A
====================
8B 7B 6B 5B 4B | 2B 1B

Becomes at the other>>

8B 7B 6B 5B 4B | 2B 1B
====================
8A 7A 6A 5A 4A | 2A 1A

Could it be possible?


So I attached mPort directly through ZX MD connection "brick", and that did the trick.

LED illuminated upon DIR MDV3_

So I now need a replacement for a suitable non cross-over cable?

Tomas

[Outsoft]

Hi,

I just wish to report that mPort works!

The problem was with the ZX ribbon cable, that I found out converts signals on EC1 port, it seems that it swaps upper signals for lower.

At one end>>

8A 7A 6A 5A 4A | 2A 1A
====================
8B 7B 6B 5B 4B | 2B 1B

Becomes at the other>>

8B 7B 6B 5B 4B | 2B 1B
====================
8A 7A 6A 5A 4A | 2A 1A

Could it be possible?


So I attached mPort directly through ZX MD connection "brick", and that did the trick.
mPort - works.JPG

So I now need a replacement for a suitable non cross-over cable?

Tomas

Great Job!

I've never thought that you need to use the Speccy MD cable to make it work

Now I'm waiting for a PCB and an External MDV unit for test it too