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This topic comprises 2 pages: 1 2
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Author
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Topic: How long can a serial cable be for plugging into a data port CP500
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 06-21-2006 02:56 AM
The RS-232 serial ports on PCs carry only data, there is no power supply line there, so even if you incorrectly wired the cable, you would be unlikely to do any damage. RS-232 does not use standard TTL Voltage levels, a positive Voltage is used to represent a logic 0 (space), and a negative Voltage is used to represent a logic 1 (mark). Both positive and negative Voltages used are in the range of 3-25V; the meaning of a transition Voltage, between -3V and 3V is undefined. All RS-232 devices must accept Voltages within this range; though the line drivers normally source lower Voltages, +/- 12V, which allows a considerable loss in transmission to still deliver an acceptable signal to the receiver.
This page gives details of the RS-232 interface.
There have been a few devices which have used serial interfaces which are similar to RS-232, but using standard TTL signal levels, but I've only ever seen a couple of these, and they were designed so as not to be damaged if standard RS-232 signals were connected.
There should be no way that Windows, or any other software, can cause a PC to output a Voltage on a RS-232 serial port that can damage another RS-232 port connected to it. This is simply not within the control of the software, it is a function of the line drivers. If the hardware was badly designed, or faulty, then this could happen, many years ago I saw a computer where loading a certain value into a certain memory location would put a direct short across one of the power supply lines, but this would apply whatever operating system the machine was running.
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