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I am trying to use a MAX3232ECPE chip to communicate between two ESP32 Feather boards, just as practice with RS-232 conversion before I move on to communicating with an actual RS-232 device. (This is mainly because the device in question is often in use by another team and I do not have hours of access to debug with it.)

I hooked up the TX/RX pins of one ESP to pins 10/9, the TX/RX pins of the other to 11/12, the R1OUT of the MAX3232 to the R2IN, and the R1IN to the R2OUT. As far as I can tell, this should convert an incoming message from either ESP to RS-232 and send it to itself, then convert that message back to TTL on the other side and send it to the other ESP. No messages are being received, however.

I am currently working on getting the oscilloscope set up to do some debugging, but wanted to ask if its even possible to hook up the MAX3232 RS-232 ports to each other before I do. I also have multiple MAX3232 chips, so if using one isn't an option can I set two up instead?

I have Vcc attached to 3V from an ESP, a 1uF capacitor between Vcc and GND, and 0.1mF capacitors between C1+/C1- and C2+/C2-. I left V+ and V- alone.

SOLVED: The answer was twofold: I had to switch my Tx and Rx assignments, so Tx1 should be pn 11 and Rx1 should be pin 12, and the same with Tx2 and Rx2. Second, like JustMe said, I had to add a 0.1 mF capacitor between V- (pin 6) and GND. Adding a capacitor between V+ and GND made no difference however.

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    \$\begingroup\$ its even possible to hook up the MAX3232 RS-232 ports to each other - Yes, it is possible. But you should draw and show us your schematic rather than describing the circuit. \$\endgroup\$
    – Eugene Sh.
    Sep 20, 2021 at 18:28
  • \$\begingroup\$ @EugeneSh. I added a quick sketch of my current wiring diagram. \$\endgroup\$
    – InBedded16
    Sep 20, 2021 at 18:44
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    \$\begingroup\$ R1OUT is a logic-level output signal and you've connected it to R2IN which is a RS232-level input. You need to connect TxOUT to RxIN. \$\endgroup\$
    – brhans
    Sep 20, 2021 at 18:44
  • \$\begingroup\$ @brhans Sorry, I used different terminology in my explanation. To go by the pinout in the datasheet, T1OUT is connected to R2IN and R1IN is connected to T2OUT, which is reflected in the wiring diagram I added. \$\endgroup\$
    – InBedded16
    Sep 20, 2021 at 18:51

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You can use it for any conversion between RS-232 levels to 3.3V levels, and even with such a loopback via itself, but without the caps on V- and V+ pins 2 and 6 it won't work as it has no caps to store the charge pump output.

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Yeah you can wire it like that if you want, but you can get muich the same result by just connecting the ESP32s directly.

For UART communication you need to cross them so RX on one unit goes to TX on the other and vice-versa.

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