Difference between flashing ESP32-WROVER and ESP32-WROVER-B

[Marcel]

Hello,

I have a board with an ESP32-WROVER powered by 3.3V and can successfully flash it using an ESP-Prog board (jumpers set to 3.3V and 100_ON/OFF is installed) connected to UART0 with the 6 pin ribbon cable using the following pinout:

Pin 1 --> 100 ohms --> EN (ESP32-WROVER-pin 3)
Pin 2 --> 100nF --> Ground
Pin 3 --> 100 ohms --> TXDO (ESP32-WROVER-pin 35)
Pin 4 --> Ground
Pin 5 --> 100 ohms --> RXDO (ESP32-WROVER-pin 34)
Pin 6 --> 100 ohms --> IO0 (ESP32-WROVER-pin 25) -- Pulled up to 3.3V using 47k resistor.

I can flash successfully using "make flash" or by pressing the BOOT button on ESP-Prog.

When I changed to ESP32-WROVER-B, I cannot flash unless I use the BOOT button on ESP-Prog. Why did I not have to press the BOOT button to flash an ESP32-WROVER, but I do have to use the BOOT button to flash ESP32-WROVER-B ? It appears that ESP32-WROVER-B has a different boot loader. Is this the reason for the difference? It also looks like the drive strength of the ESP32-WROVER is stronger than the drive strength of the ESP32-WROVER-B as rise and fall times are faster for ESP32-WROVER. Is this expected? What other differences are there between ESP32-WROVER and ESP32-WROVER-B and why?

Thanks and regards,
Marcel.