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*If* your PC has a RS232 port (with classic DB9 or even DB25 connectors), do *NOT* use it. It is specified for 5-15V and indeed 12V is/has been common. As for the 1.8V input levels: they will also be likely to go unnoticed because for the PC they are to low.
Use designated 1.8V or risk some fried chips (and a broken device) and try your luck with a 3.3V adapter. You can get them as USB-serial interfaces.
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