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I bought a GN801 GPS module from Stoton ( http://www.stotoncn.com/gnssmodule/showproduct.php?lang=en&id=42 )

Power supply range is +5V. There is an onboard MAX3232CAE that is supposed to output RS232 signal.

I need to connect this module to a third party system that only accept RS232 with -12V / +12V signals levels.

When viewing MAX3232CAE TX pin trace with an oscilloscope, i can see it outputs -6V / +6V signal.

  • Wasn't MAX3232 supposed to output -12/ +12V signal, did i miss something here ?

  • This GPS module also exists in version with TTL output rather than RS232, if i go with TTL outputs (0-5V) how could i get a real -12V / +12V RS232 output since MAX3232 looks not to do so ?

Thank you very much for your lights on this and best regards,

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    \$\begingroup\$ RS-232 is specifying voltage level for anything between (+/-)3-15V. So your device which is not accepting +/-6 is not RS-232 compliant (BTW, where is it saing it is not accepting it?). \$\endgroup\$
    – Eugene Sh.
    Sep 18 '17 at 21:29
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    \$\begingroup\$ The MAX3232 datasheet says it's only guaranteed to provide +/-5V RS232 outputs, so the +/-6V you're seeing is good. And as Eugene has pointed out, this is still well within spec for RS232. It's your 'other device' that's non-compliant. \$\endgroup\$
    – brhans
    Sep 18 '17 at 21:50
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I need to connect this module to a third party system that only accept RS232 with -12V / +12V signals levels.

You will need to supply details of that device, and a copy of the documentation which leads to the conclusion that it requires those signal levels. That requirement is not part of RS-232.

When viewing MAX3232CAE TX pin trace with an oscilloscope, i can see it outputs -6V / +6V signal.

Good.

Wasn't MAX3232 supposed to output -12/ +12V signal

No, the MAX3232 datasheet shows that it outputs a minimum of +/-5 V (with 3k load) which meets the RS-232 specification (see TIA/EIA-232-F paragraph 2.1.6).

This GPS module also exists in version with TTL output rather than RS232, if i go with TTL outputs (0-5V) how could i get a real -12V / +12V RS232 output since MAX3232 looks not to do so ?

+/-12 V is not "real" RS-232. Even a very old RS-232 driver, like the MC1488, is not guaranteed to output +/- 12 V. Although it would be possible to achieve those signal levels, it might require a design using discrete components or boosted power rail voltages for an old RS-232 driver.

In the distant past, +/-12 V was a common maximum RS-232 voltage level seen in real life. Perhaps the documentation you have for that "module" has been mistranslated or otherwise misinterpreted that this voltage is a requirement...

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