Connecting an ESP32 to the SP PRO serial port

The SP PRO serial port is RS-232 (±12 V signalling), not RS-485 and not logic-level UART. You therefore must put an RS-232 ↔ 3.3 V level shifter between the inverter and the ESP32 — wiring the SP PRO directly to an ESP32 GPIO will damage the ESP32.

Reference: Selectronic Tech Note TN0050 "SP PRO Serial Port Pin-out", cross-checked with the selpi connecting.md (which connects via an FT232 USB-to-RS232 cable at 57600 baud).

SP PRO RJ45 pinout (TN0050)

RJ45 pin	Signal	Use
1	+12 V isolated (1 A)	optional supply — do not feed the ESP32 directly
2	DTR	not needed
3	TXD	SP PRO → us
4	GND	common ground (required)
5	GND	ground (redundant)
6	RXD	us → SP PRO
7	DCD	not needed
8	—	not connected

Only TXD, RXD and GND are needed. Settings: 57600 baud, 8N1, no flow control.

Level shifter: MAX3232

A MAX3232 (3.3 V RS-232 transceiver with internal charge pump) is the right part — it is the 3.3 V-capable successor to the MAX232. RS-485 transceivers (MAX3485 etc.) are not suitable here. Add the four 0.1 µF charge-pump capacitors per its datasheet.

Wiring

  SP PRO (RS-232)            MAX3232                 ESP32 (3.3V UART2)
  ---------------           ---------               ------------------
  RJ45 pin 3  TXD  ------->  R1IN
                             R1OUT  ------------->   GPIO16  (RX2)
  RJ45 pin 6  RXD  <-------  T1OUT
                             T1IN   <-------------   GPIO17  (TX2)
  RJ45 pin 4  GND  -------+- GND ----------------+-  GND   (common!)
                          |                      |
  3.3V  ----------------- VCC                    (4x 0.1uF charge-pump caps)

TXD of one side always goes to RXD of the other — note the crossover above.
Common ground is mandatory. RS-232 is single-ended and needs a shared reference.
RS-232 has no direction-control line (unlike RS-485), so there is nothing equivalent to DE/RE to manage.

ESP32 UART

Use UART2 to keep UART0 free for USB logging/flashing:

Serial2.begin(57600, SERIAL_8N1, /*RX=*/16, /*TX=*/17);

GPIO16/17 are safe general-purpose pins on most ESP32 dev boards. (On a few modules with PSRAM these pins are reserved — pick two other free UART-capable GPIOs and update the sketch if so.) See examples/Esp32SerialMonitor/.

Quick bring-up checks

Confirm the SP PRO serial port is enabled and note its baud and password (front panel → Settings → Communications).
Loopback-test the MAX3232: short its TTL TX→RX and echo bytes through the ESP32.
With it wired to the SP PRO, the first query at 0xa000 should echo back; the sppro-console demo (or the sketch) will report "connected" once login succeeds.
If login fails, the usual causes are wrong/blank password, swapped TX/RX, or missing common ground.

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