Atari ST to Commodore 1084s monitor

Hi Amiga Enthusiasts!
A good friend from England sent me a url to this forum today to help me solve a problem I am having while trying to design a Video cable to connect what I am told is an Amiga compatible 6 pin DIN video output jack on a custom designed 6809 SBC called MAXI09 to my Commodore 1084S RGB Monitor.
I just finished reading all the messages and I must say I didn't know there were so many 'standards' out there for wiring up video cables. I knew a few existed of course, but WOW!
From the messages on this forum, I think I have figured out how to make my custom video cable, but just to make sure I have this right in my mind and on paper I will detail the connections here for your consideration and kind suggestions. Thank you all for keeping the Amiga alive. I have never been able to own one, but my interest has been peeked about Amigas for decades. Over the last several years I have heard that the Atari ST series is good too. I'd like to learn more about these 68K based computer systems.
I have been working on several 68000 SBCs called the MAXI68K and MINI68K designed and built by a friend, Roger in Washington State, USA. These are basic computer boards. The latest version of the Maxi68K has 2MB of Static ram, 1MB flash eeprom, 68681 Dual Uart driving 2 serial ports, 2 - 16 bit parallel ports, an 82C55 driving the IDE interface with a CF to IDE adapter and a 4GB Transend x133 CF Card installed for online storage. It's the CF part that is giving Roger, a fit over. It's been the bottle neck of the development lately. The MINI68K has an MC68HC000FN20 20MHZ microprocessor, 1MBs of Static Ram, 1MBs of Flash eeprom, an MC68B50P ACIA driving a serial port, and a 10 pin + 40 pin expansion bus. This Mini68K is the first of his 68K boards to have an expansion bus. I hope to learn 68000 assemble language eventually. Well there you have it, my current projects in a nutshell. I'll be going to IT Training next year for 11 months so i want to get my MAXI09 Video output functional way before then.
I am also working on a custom built 6809 SBC called the MAXI09 a fellow in England created whose name is Lawrence which brings me to this forum today.
Here is the wiring diagram I currently have put together based on what Lawrence has given me and information I have gleaned from this particular forum thread.

MAXI09 Video Output 1084S 6 pin DIN Linear RGB 6 pin DIN Input
1. Red to 4. Red
2. Green to 1. Green
3. Blue to 5. Blue
4. Sync to 2. H. Sync
and to 6. V. Sync
5. GND to 3. GND
6. +5V to nowhere.

Will this work? One person on this forum set up a cable in a similar fashion regarding the combined sync signal. I'm looking forward to communicating with all of you Amiga and Atari Experts! Whoo-Hoo! I think I have found the motherload!!! Take care my new friends.

[amigappc]

Do we know why resistors are not 75 ohms?

[pandy71]

Originally Posted by amigappc

Do we know why resistors are not 75 ohms?

You mean why there are 120 Ohms not 75? Don't know Atari ST video level and didn't checked 1084 schematics but video levels may be higher than regular expected 1Vpp and 120 Ohm resistor with 75 Ohm in 1084 may reduce voltage by 1.6 times (i.e. this form a voltage divider) commonly practiced solution. They should have no impact on bandwidth for sure as video DAC in Amiga for example use resistors from 1000..8000 Ohms range and it works up to 28MHz fine.

[Tavis]

This is exactly what I am looking for. I’m glad this thread survived and wasn’t deleted lol!

Should my cable be Shielded or would a standard 6 wire 24awg cable work ok?

Like this—> Matugajp 24awg 0.2mm² Electrical Wire 6 Core Extension Cable 10feet UL2464 DC 5V/12V/24V/300V 24 Gauge Oxygen Free Stranded Tinned Copper Wire https://a.co/d/bCpIdHO

[cloverskull]

Hmmm, wonder if the inverse of this is possible, as I have a spare Atari monitor and would love to experiment just for the heck of it!

[Tavis]

Originally Posted by cloverskull

Hmmm, wonder if the inverse of this is possible, as I have a spare Atari monitor and would love to experiment just for the heck of it!

Color? for an ST? i need it.. all i have is a commodore monitor for my ST lol

[cloverskull]

Oh nice, DM me, I'm in the Bay Area, shipping should be straightforward. I'll test it for you first and send you a few pics.

[Pyromania]

Won’t the 1084S explode in protest? You’re treating it like a P.O.W.

[Tavis]

Originally Posted by Pyromania

Won’t the 1084S explode in protest? You’re treating it like a P.O.W.

Not if it ends up in my hands. It’s will save me from making this cable and connecting my Atari ST to my Amiga monitor! Everything will be right in the world. At least my vintage electronics lab world.

[Tavis]

I just made this cable and it works perfect!
My STacy now has color when it borrows my Amiga’s monitor

[Tavis]

Hey guys, so although this cable works perfectly on my STacy 2, I have a 520 ST and the picture comes up but its scrambled diagonally and scrolling vertically.. It's got a sync issue. I also have a brand new 520 ST board I bought as a diner to troubleshoot and it has the exact same problem.

Anyone know what the cause might be?

[slaapliedje]

Originally Posted by Tavis

Hey guys, so although this cable works perfectly on my STacy 2, I have a 520 ST and the picture comes up but its scrambled diagonally and scrolling vertically.. It's got a sync issue. I also have a brand new 520 ST board I bought as a diner to troubleshoot and it has the exact same problem.

Anyone know what the cause might be?

I think there are a few sellers of these cables that hate Ataris...
I tried two new ones on my MegaST last night and got the same scrolling nonsense. But I fixed my SC 1435 last night! So now I can use that.

I did note though, in the Atari SC 1435 (which works flawlessly with the A500 as well) it has 75ohm resistors on the mainboard already.

The weird issue I have, even if I use the original 1435 cable, or yet another 'Atari ST to 1084S' cable I have bout (except the rolling screen like you have) they have a 'jumping' that happens. Like the 1084S just bounces constantly like this emoji.. and yes, I have tried multiple1084S D1 and P1s... (I kept trying to find one that worked for my STs... and it is always good to have backups!)