Atari ST Display Basics

All information relating to connecting your ST to a modern TV/monitor.
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exxos
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Re: Atari ST Display Basics

Post by exxos » Sun Mar 18, 2018 1:08 pm

I think I see the problem.. on info-coach it says the same as Ingo wrote.. but later down the page it says "12V pullup" , so the info on the site is actually wrong at the top of the page..
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Re: Atari ST Display Basics

Post by troed » Sun Mar 18, 2018 1:13 pm

exxos wrote:
Sun Mar 18, 2018 1:02 pm
I just checked pin 8 on STE & STM is via 1.2K resistor. Assuming a typo Ingo ?
It's "common knowledge" that there are somce machines that don't put out 12V ... but considering even the 520ST schematics has it I'm quite confused as to exactly which those machines would be.
12V / 10mA pin (STE) : On STE this pin is connected to 12V.
GND pin (ST) : On 520STF this pin is connected to GND
http://info-coach.fr/atari/hardware/int ... _connector

edit: Yeah you saw it as well. Actually I recall the info on that page was recently changed due to a discussion on A-F. Before that it excluded more models from 12V IIRC.

(I've started to doubt what my 520STM does. I'm currently running it on 5V only waiting for a picoPSU to arrive, so it obviously cannot put out 12V .. )

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Re: Atari ST Display Basics

Post by IngoQ » Sun Mar 18, 2018 1:15 pm

exxos wrote:
Sun Mar 18, 2018 1:02 pm
I just checked pin 8 on STE & STM is via 1.2K resistor. Assuming a typo Ingo ?
In only have a STE, the information about the 520ST having GND connected on Pin 8 is based on this pinout:

http://info-coach.fr/atari/hardware/int ... _connector

Since it is obviously wrong I corrected it.

I did a little research, and found that many sites show this wrong pin out. This page did a little research where this mistake actually came from, and it seems to be based on the Book "The Concise Atari ST Programmer's Reference Guide" by Katherine D. Peel, ISBN 1 85181 017 X.
Ingo :geek:

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Re: Atari ST Display Basics

Post by IngoQ » Sun Mar 18, 2018 1:20 pm

Yep, here it is:
2018-03-18 14_19_32-The_Concise_ST_68k_Prog_Ref_Guide.pdf.png
2018-03-18 14_19_32-The_Concise_ST_68k_Prog_Ref_Guide.pdf.png (342.92 KiB) Viewed 671 times
Ingo :geek:

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Re: Atari ST Display Basics

Post by IngoQ » Sun Mar 18, 2018 1:33 pm

What confuses me further is, that Atari calls pin 8 in their schematics "mode switch". Since it is only connected to 12V this does not make any sense to me. One could assume that this is the signal that pin4 needs to switch to mono mode. But this would be GND, so why "mode switch"?
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Re: Atari ST Display Basics

Post by exxos » Sun Mar 18, 2018 1:39 pm

IngoQ wrote:
Sun Mar 18, 2018 1:20 pm
Yep, here it is:
So we have a bit of a mystery then... At this point I would assume the image has the wrong info there.. Though unless someone comes across a ST with no 12V on pin 8.. then there must be some "early early" design out there which pre-dates even the schematics..
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Re: Atari ST Display Basics

Post by IngoQ » Sun Mar 18, 2018 1:42 pm

Found a possible explanation... SCART uses a 12V signal to differentiate between RGB and composite inputs. As you can see i.e. here, many SCART cables use pin 8 to provide these 12V. And on SCART connectors, this is actually called "mode switch".

So my theory would be, that this was actually intended by Atari. But this would leave us with absolutely no reason, why any machine would NOT have 12V on this pin.
Ingo :geek:

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Re: Atari ST Display Basics

Post by troed » Fri Mar 30, 2018 8:49 pm

troed wrote:
Sun Mar 18, 2018 1:13 pm
(I've started to doubt what my 520STM does. I'm currently running it on 5V only waiting for a picoPSU to arrive, so it obviously cannot put out 12V .. )
I guess we'll need to find someone with a 260ST to see what they had on pin 8 ;) Now with the picoPSU connected to my 520STM I can verify that it has 12V, as the schematics say it should.

/Troed

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