Null Modem Cable

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Syrax
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Re: Null Modem Cable

Post by Syrax » Thu Jun 26, 2014 5:10 pm

I give up. Got new usb to serial cable. A good Star-tech one. Still will not transfer. I am now sure it must be the null modem cable. The pin assignments must be off. How does one know when purchasing a null modem cable that the pin assignments are correct? I certainly am not going to keep purchasing these things in the random hope that one is right.
I will wait until I eventually buy an ACA 500 and use the CF card for transference.
I feel the pain of anyone who has tried this and failed. Countless hours spent in frustration. Never again.



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nonex
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Re: Null Modem Cable

Post by nonex » Fri Jun 27, 2014 3:10 pm

So you have two usb->serial adapters, no? If you have a working cable, you should be able to plug both adapters into your laptop - find out the port designations through device manager (COM3, COM4, etc), and connect them together with your cable. Then run two terminal programs at the same time, each using a different port but same baud rates, etc. When you type into one screen, you should see it in the other window, and vice versa.

Putty for Windows is a suitable win32 terminal emulator with serial support.

Serial ports are tricky. For successful binary transfers you have to matched settings, etc. Try with two terminals and see if you can squeeze out a character or two!

Now IIRC the Amiga serial port is 25pin.. the usb adapters are likely 9pin. So if you have a hardwired 9pin->25pin cable, then that is not fun. Its best to have a 9pin to 9pin cable, with a 9pin to 25pin adapter, for flexibility. The 9pin to 25pin conversion could be wrong.. The null modem crossover could be wrong... or nonexistent! the settings could be wrong.. the port you pick on your pc could be wrong... there is a lot to go wrong! If you have a fused 9to25 then you can still play, but you'll need a terminal emulator on the Amiga side.. I used to use JRterm back in the day... Aminet will be filled with terminal emulators.

If you can't get characters to show up, we'll need to diagnose the cable you have. You can use a multimeter for continuity checks or failing that a flashlight and a couple of wires. Map the pins on each side and denote how they are connected. I just did this a few weeks ago when I was making an adapter to obtain console on a device. The internets has plenty of numbered pin diagrams you can print out for your mapping pleasure.

Also, If you have an old modem in your box-of-tricks, you can use that with a straight through cable to test out your serial ports/adapters... They'll happily talk to you.

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Re: Null Modem Cable

Post by Syrax » Fri Jun 27, 2014 5:10 pm

Thanks for your reply:
As for a terminal program, I have been using amiga explorer. I have talked to others that highly praise this program. The setup program, gives succinct directions for the serial pref settings on both sides; PC and Amiga. The port setting is the same for the program, and the usb to serial adapter as seen on the device manager prefs.
The Amiga Explorer page, gives trouble shooting instructions, and in this gives specific pin placement for the null modem cable: http://www.amigaforever.com/kb/13-105
The null modem cable I have, is molded. I cut the molding off, and examined the pins; they do not match at all (thus wrecking the cable, but I was curious). Apparently at one time, null modem cables, could be conveniently disassembled, and resoldered.
I have found an Atari computer dealer selling a null modem cable, and am awaiting a response concerning pin placement, but to tell the truth, I have about given up. I plan on taking the new, usb to serial adapter back to Best Buy (Star-tech) an recoup the $20. There was a time, when parts were much more available for projects like this. Unfortunately those days are gone.

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nonex
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Re: Null Modem Cable

Post by nonex » Fri Jun 27, 2014 7:52 pm

This isn't a trip to the moon, so I don't know why you would "give up". We're only talking about ensuring some wires (three would do!) hit the right pins between two computers. How hard is that?! I mean, if you're desperate, you can forgo plugs and all and just tape the wires to the pins! You have some wire around, no?

Why you would cut the molding open to check the connections is beyond me -- you can tap into the cable at either end -- no peering inside required! If it came to be, after mapping out the "current" connections, that a mod was needed, we could have cut the cable in half and likely rewired it. Still, you have some parts you can work with. And I'd use what you can.

As with any problem solving, you need to walk through a checklist.

1. Does the PC serial port work
2. Does the Amiga serial port work
3. Are the right pins connected between ports
4. Is the software talking to the ports
5. Are the settings the same on both ends
6. Flow control: Am I using RTS/CTS when they possibly aren't wired, XON/XOFF or no flow control...

You can pretty much assume your usb adapter and Amiga ports are good, but if you've never successfully used them, you just don't know! You need to demonstrate them working with something.. And the cable, you can't know how it is wired until you check the wiring yourself.

But like I said, three wires is the bare minimum to get a connection established between two computers. I'm sure you can pull it off and have two terminal programs talk to each other. When you get that working, try the fancier software.

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Re: Null Modem Cable

Post by Syrax » Sat Jun 28, 2014 1:12 am

To tell the truth, I am not all that obsessed with it. Eventually, I will get a ACA 500. Once I have that it is a simple matter of transferring files from my PC to the CF card. No biggie. This was just something I wanted to try, but with all my real life tasks, the last thing I want to get involved with is temporary soldering, just to prove it can be done. Some people were curious as to how successful I was in my endeavor, and I have responded.

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Re: Null Modem Cable

Post by iced_nine » Sat Jun 28, 2014 3:42 pm

I'm in the same boat when it comes to finding a good null cable that works without having to pull out a schematic... my settings are correct on both ends... I know amigakit.us sells one and I would assume that it is wired correctly seeing how they deal with all Amiga HW, but they are out of stock and they never seem to reply to e-mail inquires...
Commodore 64/Amiga 500 Enthusiast

Syrax
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Re: Null Modem Cable

Post by Syrax » Wed Jul 09, 2014 3:35 pm


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Re: Null Modem Cable

Post by iced_nine » Sat Jul 12, 2014 8:05 pm

Ordered - good to know one out there works.... thanks for the link!
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Re: Null Modem Cable

Post by iced_nine » Mon Jul 28, 2014 4:02 pm

How's that cable working? No issues like the previous ones tried?
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Syrax
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Re: Null Modem Cable

Post by Syrax » Mon Jul 28, 2014 5:31 pm

Absolutely no issues. If you are having problems, some words of advice. Use the setup on the Amiga Explorer program. Just right click on the Amiga Explorer shortcut and follow the instructions. I did change the "packet size" to 512 from 19200. Found this info on a forum and it works great. It may take longer, but my adfs transfer perfectly. The Amiga Explorer program, though shareware, is not disabled in any way. I bought a key, but there is not any place to input it....lol. But I supported the developer. Let me know if you are having any probs and where in the setup procedure?

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