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December 10, 2016, 07:47:37 07:47


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Author Topic: RS-232 cable connetion detector ?  (Read 1053 times)
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elcielo
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« on: May 14, 2014, 05:13:51 17:13 »

I want RS-232 cable connection detector.
like /INVALID pin of MAX3221
plz help me.
« Last Edit: May 14, 2014, 05:31:41 17:31 by elcielo » Logged
Gallymimu
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« Reply #1 on: May 14, 2014, 10:46:31 22:46 »

most RS232 connections are idle high, so maybe you can look for a high signal for some period of time to detect?
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cusna
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« Reply #2 on: July 24, 2014, 03:17:34 15:17 »

http://www.arcelect.com/rs232.htm
Wwith a good oscilloscope is unable to locate the pins.
are the easiest to find rx and tx (which are also the most important Smiley)
These pins will find them immediately because usually there 'activity and then change state (1-0-01 ...) often.
Another thing to understand is who is who is the DTE and DCE so that you know that:
pin TxData (from DTE) when no data is at level 1
the condition of level 1 has a voltage between -5 and -15 V
while the condition of logic 0 has a voltage between 5 and 15V
(it is a negative logic)
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rtm
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« Reply #3 on: July 24, 2014, 09:44:58 21:44 »

RS232 is simple: line is -5 to -12V when resting, and +5 to +12V when sending.

You can find description of /INVALID output in datasheet of MAX3221. It is simple:

Quote
The INVALID output notifies the user if an RS-232 signal is  present at the receiver input. INVALID is high (valid data) if the receiver input voltage is greater than 2.7 V or less than -2.7 V, or has been between -0.3 V and 0.3 V for less than 30 ms. INVALID is low (invalid data) if the receiver input voltage is between -0.3 V and 0.3 V for more than 30 ms.

So, in simplest way, you need to find if signal is out of range between, let say, from -2V to +2V. You can do it with 2-wire dual colour light diode. It will be one colour if line is in "0" state, or other colour when line is in "1" state. And RS232 connection will be absent if the diode is black.

There is the circuit of RS232 Break-Out Box using such method, that allows to monitor the state of all lines:


Full article about that device is here: http://www.marcspages.co.uk/tech/3105.htm

May be it will be enough to monitor only one the "TX" line in your case.
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