Can't set character match bits in USART_CR2

[osmaneralp]

Posted on April 18, 2014 at 02:58

I'm trying to generate a reset on a USART receive character match on the F3 Discovery board. If I understand the user manual, I need to set bits 31:24 of USART_CR2 to be the character I want to match. The problem is that I cannot change those bits. I can change other bits, such as bit 23 of CR2. I made sure I set RE=0 as the user manual says to do. Is there something else I need to do to set the match character? Does anyone have code that generates an interrupt on match?

Here is how I was trying to set the match character:

  uint32_t reg;

  reg = (uint32_t)USART1->CR1;

  reg &= (uint32_t)0xfffffffb;

  USART1->CR1 = (uint32_t)reg;  // This works. I can read back the changed value.

  reg = USART1->CR2;

  reg |= (uint32_t)0x96000000;  // A tilde character

  USART1->CR2 = (uint32_t)reg; // This does not work. CR2 is unchanged.

Any suggestions would be greatly appreciated!

--Osman

#character_match #usart_cr2

[osmaneralp]

Posted on April 18, 2014 at 03:28

I've been working on this problem all day, and (of course) I solve it five minutes after posting here. It seems that the User Manual is incorrect: setting RE=0 does *not* allow you to modify bits 31:24. You have to set UE=0. After I did that, I could set the match character and now my interrupt works. I hope this info helps someone else.