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Author Topic: Maximum Serial Cable length?  (Read 8676 times)

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Offline jibelingTopic starter

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Maximum Serial Cable length?
« on: March 31, 2008, 01:33:14 PM »
Anyone have any idea/experience with RS-232 cable? What is the longest cable length possible with a 19200 bps data rate? There has to be someone that has tried this out.

John

Offline jibelingTopic starter

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Re: Maximum Serial Cable length?
« Reply #1 on: March 31, 2008, 03:49:25 PM »
Never mind found my answer.

Offline airman00

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Re: Maximum Serial Cable length?
« Reply #2 on: March 31, 2008, 05:29:13 PM »
Never mind found my answer.

please post your answer and not just say that you found it. It might help out other people.
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Offline Webbot

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Re: Maximum Serial Cable length?
« Reply #3 on: March 31, 2008, 07:32:07 PM »
From http://www.lammertbies.nl/comm/info/RS-232_specs.html

Quote
Cable length is one of the most discussed items in RS232 world. The standard has a clear answer, the maximum cable length is 50 feet, or the cable length equal to a capacitance of 2500 pF. The latter rule is often forgotten. This means that using a cable with low capacitance allows you to span longer distances without going beyond the limitations of the standard. If for example UTP CAT-5 cable is used with a typical capacitance of 17 pF/ft, the maximum allowed cable length is 147 feet.

The cable length mentioned in the standard allows maximum communication speed to occur. If speed is reduced by a factor 2 or 4, the maximum length increases dramatically. Texas Instruments has done some practical experiments years ago at different baud rates to test the maximum allowed cable lengths. Keep in mind, that the RS232 standard was originally developed for 20 kbps. By halving the maximum communication speed, the allowed cable length increases a factor ten!
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Offline jibelingTopic starter

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Re: Maximum Serial Cable length?
« Reply #4 on: April 01, 2008, 11:14:25 AM »
I found the same site as Webbot. If a longer distance than 50 feet is needed, slow the bit rate down and you can go much longer apparently.

Offline izua

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Re: Maximum Serial Cable length?
« Reply #5 on: April 01, 2008, 01:36:35 PM »
Or better yet, use a higher voltage (up to the specs, of course) or get a better chip with a higher slew rate (max232A instead of max232 f.i.)
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Offline Admin

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Re: Maximum Serial Cable length?
« Reply #6 on: April 06, 2008, 01:10:17 PM »
Just to add to this post, I couldn't get much more than 10ft at 115200bps.

(and it took me like 4 months to figure out that it was cable length causing everything to fail :'()

 


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