+-----+
+------------| USB |------------+
| +-----+ |
(Built-in LED) | [ ]D13/SCK MISO/D12[ ] |
| [ ]3.3V MOSI/D11[X]~| [LED Blue]
| [ ]V.ref ___ SS/D10[X]~| [LED Green]
Reset Out | [X]A0 / N \ D9[X]~| [LED Red]
Reset In | [X]A1 / A \ D8[X] | [Single Pin Led]
JP3/4 (Video Mode) | [X]A2 \ N / D7[X] | Pad Port Pin 1
JP1/2 (Language) | [X]A3 \_0_/ D6[X]~| Pad Port Pin 2
[LCD SDA] | [X]A4/SDA D5[X]~| Pad Port Pin 3
[LCD SCL] | [X]A5/SCL D4[X] | Pad Port Pin 4
| [ ]A6 INT1/D3[X]~| Pad Port Pin 6
| [ ]A7 INT0/D2[X] | Pad Port Pin 7
+5V | [X]5V GND[X] | GND
| [ ]RST RST[ ] |
| [ ]GND 5V MOSI GND RX0[X] | Pad Port Pin 9
| [ ]Vin [ ] [ ] [ ] TX1[ ] |
| [ ] [ ] [ ] |
| MISO SCK RST |
| NANO-V3 |
+-------------------------------+
hello
acording to docs tx and rx pins are swapped in the drawins on the wiki
https://github.com/SukkoPera/MegaDrivePlusPlus/wiki/Chip-Preparation#wiring
thanks