Associate

Question

STM32F105 Shared Pin PA9 (USART1-TX and VBUS) conflict

2 replies
764 views

Posted on January 05, 2014 at 19:36

Hello,

the STM32F105 Device share USART1-TX and VBUS for USB on Port PA9.

I need the USART1 for communication and for the internal Bootloader (only USART1 on my used 64pin Devices possible), if the firmware corrupts.

I need the USB-Device possibility for connecting the Device to a HOST-PC sometimes, but its not used for the internal Bootloader.

The other STM Devices with only USB-Device function don�t have a VBUS port und use an external resistor for USB recognition.

My question is: Can I switch off the VBUS - Port on PA9, still use the STM32F105 as a USB-Device (with external USB Resistor), and use the PA9 for the USART1-TX?

Thank you

Rheinhold

#stm32f105-pa9-usart1-vbus

UART-USART

This topic has been closed for replies.

chen

Associate II

Posted on January 06, 2014 at 10:43

Hi

''Can I switch off the VBUS - Port on PA9, still use the STM32F105 as a USB-Device (with external USB Resistor), and use the PA9 for the USART1-TX?''

Yes you can BUT the VBUS will but toggling while it is being used as USART Tx and USART Tx will be held high/low while being used as USB.

You could also electrically cross couple the USB to UART.

(I presume you will be using something like a MAX232 for RS232 level shifting)

Is this OK behaviour for your application?

To overcome this, you could use a IO pin and a buffer (try a 4 port ananlogue buffer) device and route one function through the buffer and disable one of the functions when you do not want it.

ralfAuthor

Associate

Posted on January 10, 2014 at 12:11

Hello,

thank you for your answer.

I have designed a switch between USART and VBUS and a Port Pin to switch USART to the alternative Pins after the Firmware is running and switch VBus to the VBUS pin.

I hope, it will works.

Thank you

Reinhold

Sign up

Click below to sign in

Login to the community

Click below to sign in