1. Recently, I want to use Edison (mini breakout) to read serial data from STM32 (3V3 ttl level), can I directly connect the TX and RX from STM32 to my Edison?
2. Furthermore, I have tried to directy connect the STM32 to Edison for Arduino expansion, but i cannot received any data. I think the parameter was correct, Band rate was 115200. Here is my connection:
STM32 RX<--------->TX Edison for Arduino
3. So I guess maybe that's related to TTL level.
The Edison module operates at 1.8V. You need a level translator, probably, a bidirectional one.
You probably have to initialize GPIOs on the Arduino module. They have different modes. Check the Arduino for Edison documentation about pinmuxing.
Here's the documentation with all these specifications. This is the http://download.intel.com/support/edison/sb/edisonmodule_hg_331189004.pdf Edison Module Hardware Guide, with all the information about its operation, and this is the http://download.intel.com/support/edison/sb/edisonarduino_hg_331191007.pdf Edison Arduino Board Hardware Guide where you can check instructions on how to initialize the GPIO as Vincenze mentioned.