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Puzzled by USART behavior

Question asked by turk.andy on Aug 14, 2012
Latest reply on Aug 15, 2012 by turk.andy
I'm porting over some code that I previously ran on Stellaris hardware to an F4Discovery board. I hooked a logic analyzer up to take a peek at what my USART code (with hardware flow control) was doing and found something I hadn't seen before.

RTS is going high at the end of each byte received by the MCU. I'm pretty sure that didn't happen with the Stellaris setup (I'd check it, but re-wiring the logic analyzer to another board is a pain).

I'll admit that the whole RTS/CTS thing drives me into dyslexic confusion, but it seems odd that either end of the connection would be signalling RTS at the *end* of a transmitted byte. Isn't flow control more useful before the data is sent?

Here's a screenshot from the logic analyzer:
http://turkish.smugmug.com/Electronics/Panasonic-13XX/24660876_PQSq5Z#!i=2025474323&k=pn5dqwm

The code is using USART3 with TX/RX on PD8/PD9 and RTS/CTS on PB14/PB13.

PS. Is there any way to include an image directly in a forum post? I tried the help link, but it brings up some generic MS help system.

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