And here’s with a 10K pull-up on RXD which indeed removes the glitch successfully…
I guess it’s an underlying STM32 problem that the frame-error (no stop bits detected) error ends up in the receive fifo as a valid byte. I’m normally working with LPC devices and have never seen that behaviour (also without pull-up) Tranceiver used is a MAX3430 with 1/4 loading on the bus.
This is just a test rig with an IMP001. Actual design will use IMP005 or IMP004m. Could you automatically enable an internal pull-up on the RXD pins if they get configured as part of a UART ?