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STM8L serial half duplex problem

sawa
Associate
Posted on May 16, 2013 at 08:18

Hi,

I have a problem with USART half duplex.  The output from my STM8L device is too strange.

0690X00000604zlQAA.png

The first half (about 10 bytes) is from host.  My device can receive this well.  After that, the host is wait to receive the data from my device immediately.

When my device starts to send back data to the host, the signal level is down about 300uSec.  After that, the level is back.  What is this ???

I try to do same thing with full duplex mode with connected Tx-Rx.  It looks like work well but same level down is happened between host changed Rx and my device changed Tx.

I try to set the mode of GPIO on same pin to both floating input and open drain output.  But the result is same.

I try to use remapped USART (PC5-6).  But the result is same.

I have another device that is not STM works well.....Oops.

Does anyone know what is wrong with me ?  Any suggestion is welcome.

Best Regards,

Zak

#stm8l #half-duplex #usart
2 REPLIES 2
mtien888
Associate II
Posted on August 31, 2013 at 00:13

You probably need to post the source code in order to find help.

Stm32User
Associate II
Posted on September 25, 2013 at 11:51

The host is slow in tri-stating the line after transmission it appears to be pulling it low for a while. When your device enables its transmitter and tries to pull it high the voltage goes to the mid point. You can see later on when the host eventually tristates that the levels recover.