SIO2PC Cable Length Question

[Tempest]

Is there any limit on the length a serial cable can be for an SIO2PC cable? The reason I ask is that I have a 8 ft serial extension cable that works just fine but I have another that's 12 ft that doesn't seem to work at all. The 12 ft one could actually be bad since I got it off the junk pile at work, but before I go an order a new one (I'm thinking 15 ft should be more than enough) I wanted to make sure there's no limitation on the length. Also, is there anything else I need to look for or will a stand serial extension cable work just fine?

[Mathy]

Hello Tempest

 

IIRC, 3 meters is actually the maximum for an RS232 cable. 3 Meters would be approximately 10 feet.

 

Sincerely

 

Mathy

[Tempest]

Wikipedia says 50ft.

 

http://en.wikipedia.org/wiki/RS-232

 

Or is the 10ft something special with the whole SIO2PC thing?

[Joey Z]

Hello Tempest

 

IIRC, 3 meters is actually the maximum for an RS232 cable. 3 Meters would be approximately 10 feet.

 

Sincerely

 

Mathy

Where did you find that information? RS232 is specifically made to work well over long-ish distances. The levels are supposed to be +/- 12 to 15 volt output and the recievers take an even wider range as valid, +/- 3 to 25V. I've used a 25 foot rs232 cable, in addition to 50 feet of in-wall wiring with my SIO2PC, for a total of 75 feet without any problems. On top of all of that, the cable wasn't 'data cable' it was phone line. all of it. 15 feet will work fine.

[Mathy]

Hello guys

 

IIRC they told me back when I was in school. Unfortunately, not everything they tell you in school is true. The real problem is finding out what is and what isn't...

 

Sincerely

 

Mathy

 

PS yes, RS232, not SIO2PC-specific. Signal levels would drop over the length of the cable.

[Tempest]

So can I just buy a generic 15ft serial (RS232) cable from Monoprice and have it work then? Nothing special needed?

[ricortes]

hehe, technically SIO2PC isn't RS232. If you use a SIO2PC USB it never is. Just ttl/CMOS logic level. At best the MAX232 version built into an Atari would be RS232 after the first 3" or so.

[Tempest]

Is there any reason I can't plug two 6ft cables into each other to get a 12ft cable? That would be easiest since I already have one 6ft cable and new ones on ebay are cheap.

[flashjazzcat]

Is there any reason I can't plug two 6ft cables into each other to get a 12ft cable? That would be easiest since I already have one 6ft cable and new ones on ebay are cheap.

None I can think of, as long as the connections are sturdy. I used to use two 3ft serial cables joined together without any issue.

[UNIXcoffee928]

After reading this, my question is:

 

"What is the maximum reliable length that a standard Atari SIO cable can be?"

 

I don't recall ever seeing that information documented anywhere. Has anyone ever made any ridiculously long SIO cables?

[+orpheuswaking]

I have a 20 foot serial cable conected to a 6 foot SIO cable and it works fine.

[Subby]

After reading this, my question is:

 

"What is the maximum reliable length that a standard Atari SIO cable can be?"

 

I don't recall ever seeing that information documented anywhere. Has anyone ever made any ridiculously long SIO cables?

I researched this a while back also, and I didn't find any info either.

[ricortes]

Here I go again on what is more of a nag then useful information. Google rs232 standard and you get 8,510,000 results. I would estimate 8,509,900 of them are outright wrong or incomplete. Most make assumptions that are wrong.

 

This is a bit nit picky on my part, but the way standards are written is seldom maximum reliable length. It will be minimum reliable length. Point being, if you say minimum reliable length then there is no maximum specified. Get my point? I am going to say from foggy memory I recall reading something like 25' minimum. That's not to say you couldn't get it to work at a low BAUD rate for a couple of miles/kilometers, it is just the minimum you have to hit. I kind of think that is what you are asking indirectly and my recollection is ~25'. Once again, every engineer I have ever met goes for a safety factor of +20% to +500% which would mean they are designed at least for 30' and guaranteed for 25'. Three standard deviation kind of thing depending on manufacturing process: You accept ~1/1,000,000 chance of not making specs.

 

I took a pic of a 30 year old manual I had laying around. It had a copy of the specs for drive and logic levels. There has always been the assumption the 1489 and presented different loads on the SIO chain. Actually the load is specified in the standard and they both meet it. I could look around because I think I have even older references that include distance figures but what I am doing with this pic is giving you something that is older then the web so you can see how 8 million+ references are incomplete. So, do you want to trust me albeit with a rusty memory or the 8 million knuckleheads that repost incomplete and erroneous data? Please don't make me find my 25' reference! Heck, it would probably change for different cable types like "Twisted Pair" anyway. 25' was probably written when we were still hooking up 110 BAUD serial printers to Liquid Scintillation Counters. If anyone asks, just say some crazy old coot said 25' and leave it at that. If you want an authoritative answer, ask Mr. Savetz to include it as a question on his podcast interviews. I'd certainly defer to the original designers of POKEY.

Edited May 2, 2015 by ricortes