diff --git a/src/nano/README.md b/src/nano/README.md
index 4f6f0cd..9cf7643 100644
--- a/src/nano/README.md
+++ b/src/nano/README.md
@@ -78,3 +78,4 @@ pinout.
 | ROW_RESET | D13 |
 | ROW_SET | A5 |
 | Serial RX | D0 (from ESP32 TX) |
+| Serial TX | D1 (to ESP32 RX, through a 5 V → 3.3 V voltage divider). Optional: needed for `READY`. Without it, the ESP waits the full 3 s timeout. |