Amiga to Amiga link cable

Hello everyone,

First time caller, long time listener.

My brother has just acquired an Amiga 600 to go along with his Amiga 500.
Of course, he has seen videos of two Amigas linked and wants to play two player Lotus 3 with his kids.

I'm pretty certain that a null modem cable is required and was prepared to follow the Amiga Forever guide on null modem serial cables for DB25 at both ends.

I know I have to put female DB25s on each end of the null modem cable and even found the casing for them cheap as well.

What I'm after is confirmation that the A500 and A600 have the same serial pinouts and that the Amiga Forever DB25 to DB25 diagram would be correct.

The last thing I want to do is make a cable up, send it to him and fry both Amigas

Unfortunately, I do not have two Amigas to test it out with.

If I could get some guidance from the Guru Meditators on this forum, I would forever be grateful.

Thanks,

Mac.

[watsonfmly]

The serial ports are the same. I bought a null modem adapter from my local small computer store. It worked great for Amiga Forever. I don't know anything about Lotus 3 though.

[basshead]

Originally Posted by watsonfmly

The serial ports are the same.

+1. Don't forget to swap the RX and TX connections when soldering

Thanks guys, will make one up using this pic from Amiga Forever.

[prowler]

Originally Posted by TheMacOne

Thanks guys, will make one up using this pic from Amiga Forever.

Way to go!

[kipper2k]

Gotta play Stuntcar racer with this, it's da best!!

[Supamax]

Is there a list of games which support linked play via serial cable?

(I didn't even know that Lotus 3 supports that! And Stunt Car Racer too! Wow!)

[Nekoniaow]

Originally Posted by TheMacOne

Thanks guys, will make one up using this pic from Amiga Forever.

If you want to achieve good speeds make sure to use a shielded cable, it's important to get as little noise as possible on a serial line: every bit has a high overhead so you want to transmit them as reliably as possible. Recycling a video cable is probably a good idea since they are heavily shielded.

In passing, I have always wondered why games tended to use serial communication instead of parallel when the latter is so much more bandwidth efficient: at least 8 times less interrupts makes for a much reduced overhead. I guess parallel cables were more expensive in these times but still. They could at least have offered both options, it's not as if one is harder to code than the other.
(Actually, I do not really wonder, I have my opinion about it. )

Originally Posted by Nekoniaow

If you want to achieve good speeds make sure to use a shielded cable, it's important to get as little noise as possible on a serial line: every bit has a high overhead so you want to transmit them as reliably as possible. Recycling a video cable is probably a good idea since they are heavily shielded.

Does the shielding need to be tied to the casing at all to be effective? Or sent to a specific ground pin?

My feeling is that it doesn't and shouldn't go to a ground pin of any shape or form, but would like to confirm.

[BigFan]

Originally Posted by TheMacOne

Does the shielding need to be tied to the casing at all to be effective? Or sent to a specific ground pin?

No.

[prowler]

Originally Posted by TheMacOne

Does the shielding need to be tied to the casing at all to be effective? Or sent to a specific ground pin?

My feeling is that it doesn't and shouldn't go to a ground pin of any shape or form, but would like to confirm.

It doesn't have to be connected, but it's good practice to tie one end of the shield to the casing (provided it's not plastic ), usually by folding it back inside the cable clamp.

Originally Posted by prowler

It doesn't have to be connected, but it's good practice to tie one end of the shield to the casing (provided it's not plastic ), usually by folding it back inside the cable clamp.

And if the casing IS plastic, would it be wise to tie it back to the metal housing on the DB25 itself?

[roy bates]

Originally Posted by TheMacOne

And if the casing IS plastic, would it be wise to tie it back to the metal housing on the DB25 itself?

the shield is the outer metal part of the plug and its connected to ground.

you can solder a wire between the two inside the plastic hood on the other side of the metal plug.if you want to.
but its not really needed.

[lesta_smsc]

I believe Lotus Turbo Challenge 2 also supports serial connection! ... I was missing out! But thanks to FS-UAE, we can now run via netplay!

For those looking for a list of Amiga games that support serial connection: http://eab.abime.net/showthread.php?t=62233

[xArtx]

If you have shielded cable it’s not a bad idea to connect the outer metal parts of the
D connector together with it. That makes connection to the RF shielding of both computers
and completes the cage between the two. There’s little point unless you use the shield conductor of the cable.

I just got Stunt Car Racer serial linked between A500 & CD32 just now
It obviously only uses the Tx/Rx lines with no flow control, because that’s all the CD32 has.

[Supamax]

Originally Posted by xArtx

If you have shielded cable it’s not a bad idea to connect the outer metal parts of the D connector together with it. That makes connection to the RF shielding of both computers and completes the cage between the two. There’s little point unless you use the shield conductor of the cable.

I would do that only if both computers are plugged to the same mains AC socket.
Otherwise some voltage differentials could arise... am I right?

[kipper2k]

Me and my neighbour used to play Stunt car Racer all the time, we ran a 50 ft 4 core solid copper telephone cable across our back yards and it worked well

[xArtx]

Originally Posted by Supamax

I would do that only if both computers are plugged to the same mains AC socket.
Otherwise some voltage differentials could arise... am I right?

Say what? All Amigas have linear power supplies and their transformers isolate them from mains.
All peripherals other than joysticks, etc. that are not switching at speed do the same thing.

[prowler]

Originally Posted by Supamax

I would do that only if both computers are plugged to the same mains AC socket.
Otherwise some voltage differentials could arise... am I right?

It's not good practice to connect both ends of the shield to ground in any circumstances to obviate the risk of establishing a ground loop, though I'm not sure that this would necessarily give rise to voltage differentials.