# 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"](https://www.selectronic.com.au/documents/TechNotes/TN0050_02%20SP%20PRO%20Serial%20Port%20Pin-out.pdf),
cross-checked with the [selpi `connecting.md`](https://github.com/neerolyte/selpi/blob/main/docs/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:

```cpp
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 `esp32/sppro_esp32.ino`.

## Quick bring-up checks

1. Confirm the SP PRO serial port is enabled and note its **baud** and **password**
   (front panel → Settings → Communications).
2. Loopback-test the MAX3232: short its TTL TX→RX and echo bytes through the ESP32.
3. 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.
4. If login fails, the usual causes are wrong/blank password, swapped TX/RX, or missing
   common ground.