Getting back data on UART when receiving board is turned off

[adamaynard]

Hello,

I have two ESP32 boards (ESP32-WROOM and ESP32-WROVER) connected via UART (I'm using pins 5 and 4 for TX and RX on both boards, and these are the only pins that are connecting those two devices).
I am sending data from ESP32-WROVER to ESP32-WROOM and everything works fine. But if I turn off the power of ESP32-WROOM, and send data from ESP32-WROVER, I am getting back what I have sent.
It feels like there is a short circuit between TX and RX on ESP32-WROOM when the power is turned off on it, and I get back what I send. When I unplug one of the cables from ESP32-WROOM that are connecting these two devices, this behavior stops.
Anyone has an idea what's happening?

[ESP_LJH]

Could you say clearly which GPIO do you use, not pin number.

[adamaynard]

pins.jpg (105.43 KiB) Viewed 1044 times

I am using GPIO 4 and GPIO 5 (they are marked as D4 and D5 on actual board).