Where is USART1 RX pin (PA10) connected to in STM32F429 discovery

[Sammalisto.Pauli]

Posted on May 08, 2016 at 00:51

I am trying to receive serial data via USART1 in STM32F429 discovery, but something is holding PA10 high so strongly, that MAX3232 cannot drive it down.  According to the schematic there should not be any pullup resistors or something.  SB15 is not fitted.

#stm32f429-discovery-usart1

[Tesla DeLorean]

Posted on May 08, 2016 at 02:06

I'd guess you're connecting to the wrong pin on the header.

[Sammalisto.Pauli]

Posted on May 08, 2016 at 11:42

Thank you clive for your reply.  I have checked the pin several times.  If I power the MAX3232 with 5 v, it works, but with 3.3 v pulses are only from 3.3 v to about 2 v, and 2 v is too high to trigger USART1.  The resistance somewhere is about 330 ohm to 3.3 v.  Pull up, pull down, no pull, no change.

I made a IO toggle program.  PA10 goes from some 0 to 2.3 V but PA9 from 0 to 3 V, as both should.  So there is something hindering PA10 to work properly. I also tested the program with STM32F407 discovery, and there is no problem, signal changes  from 0 to 3 v