3 ms·
> oops, just connected 12V RS-232 to a 3.3V device Maybe or maybe not. I ran 12V RS-232 levels into a 5V Atmel 8515 for a year or two 24/7 without issues, and
by Scoundreller 4y ago
> oops, just connected 12V RS-232 to a 3.3V device
Maybe or maybe not. I ran 12V RS-232 levels into a 5V Atmel 8515 for a year or two 24/7 without issues, and tens of thousands, maybe more, have too. And that's a CMOS part.
(This was for a paytv interface sitting between an iso7816 slot and an x86 based emulator. The Atmel 8515 did the inversion in software).
The RS-232 on the PC side would have no issues with interpreting +5 as logic0 and 0V as logic1.
Some would setup a Max232 or Max233, but it wasn't necessary.
Others would use an MC1489 to at least convert the -12V and +12V into 5V and 0V by doing an input and then output into the chip, but again, it was out of caution and not actually necessary.
- exmadscientist 4y agoYou can sometimes get away with this if your cables are short and your EMC environment is gentle. (An EE wouldn't try it, but only because sticking the transceiver in is quite easy.) You can never get away with this if your cables are long and your EMC environment is hostile. That's why we have 232 and, especially, 422/485: for when the job is hard.
- Scoundreller 4y agoDid it over ~100' of dollar-store grade RJ-11. (Maybe that's long, maybe that's short, depends on perspective). Was a residential environment, so EMC situation was nothing like some industrial environments.