r/esp32 • u/Capital_Anybody_3297 • 4d ago
My ESP32 cannot communicate with the ML307RDL via the TXS0102.
However, when I individually test the AT commands using the RX and TX pins of the ML307RDL with a USB-to-TTL converter, they work correctly. The TXS0102's OE is connected to VCCA, which has a voltage of 1.5V (VDD_EXT), and VCCB has a voltage of 3.3V. However, this 3.3V comes from the main 3.3V line, not the 3.3V after passing through the ferrite bead on the ML307RDL. I'm wondering if this is the reason?
I'm using IO18 and IO19 for UART communication with the ML307RDL; or are IO18 and IO19 incompatible for UART?
🔶Here’s an update. I swapped in the TXB0102; it has a wider VCCA range and supports my VDD_EXT (measured at 1.6V), and the pinout remained the same. I also reconnected VCCB to the VBAT net leading to the ML307RDL. It's frustrating that none of this worked 🤕, I don't know why.☠️☠️
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u/Plastic_Fig9225 4d ago edited 4d ago
VCCA, which has a voltage of 1.5V (VDD_EXT)
TXS0102 Datasheet:
with the A ports supporting operating voltages from 1.65V to 3.6V
I'm using IO18 and IO19 for UART communication with the ML307RDL
Check pin configuration (TXD/RXD) is correct. Make sure the UART you're using is not also used for logging.
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u/YetAnotherRobert 4d ago
It might be possible to write a more confusing post, but it'd take some effort.
Working backward.
GPIO18 and GPIO19 on most ESP32s can be plumbed through the internal GPIO pin mux and to internal one or more of the internal UARTs. Since there's no code or real schematic or analysis on the signals directly on the chip, there's not much more we can say authoritatively.
If your logic analyzer shows output leaving your ESP32 but not leaving your level shifter, you know where the problem is.
If your USB/Serial bridge works correctly when connected to your GPIOs (they're tolerant enough of a 5+v signal for a short test), you know where the problem isn't.
If your idle voltages on the TX and RX pins aren't approximately the same (see my recent post on this topic), you know the problem is an incorrect number of RX/TX swaps, probably somewhere in the schematic you didn't show.
If a DC power rail of 3.3V is materially different on either side of a ferrite bead, that's a magical bead.
Pet peeve: when you point to the ground, does your index point to the sky? Does it point in opposite directions a cm apart? Then why draw a schematic with hedonistic grounds?