Sharing PA5 between HS USB and DAC2 on STM32F4

[sbsohrabi]

Posted on August 16, 2014 at 06:06

Hi

I have problem in sharing the PA5 functionality on STM32f407IGT6.As I need to use both of DACs in my design, and HS_ULPI_CK is also routed only on that pin (there is no multiplex to any other pins).I can not use OTG_HS and DAC2 simultaneously .Please give me a solution.another question : what is HS_ULPI_CK direction. Is it input clock of the MCU on HS USB ?

[frankmeyer9]

Posted on August 18, 2014 at 11:05

Sorry, but basically the ''shared'' functions of a GPIO pins are mutually exclusive, you can have just one at a time.

Please give me a solution. Check the datasheets of the 144/176 pin package versions, these two peripherals might be routed to different pins there, and not clash. If so, get a board with the corresponding package. Otherwise, consider an external DAC.

[sbsohrabi]

Posted on August 21, 2014 at 10:44

thanks. I know I can not have two functions on one pin simultaneously.

But It's and odd situation.You mean we can not have High speed USB and DAC2 in an applicaiton together ?It's the case. I looked at datasheet, and no other pins at the chip has these functionality I told about.the package is 176 LQFP

[frankmeyer9]

Posted on August 21, 2014 at 13:52

You mean we can not have High speed USB and DAC2 in an applicaiton together ?

It's the case. I looked at datasheet, and no other pins at the chip has these functionality I told about. the package is 176 LQFP I did not check your issue myself, but it might well be the case. Especially I never designed USB  periphery, just used the onboard USB design on discovery boards. But I remember some UART units wich have 3 different options for each TX and RX. It is worth checking carefully if the conflicting USB functionality is not routed to another output. However, an external DAC is still an option. While ST's DAC implementation is quite good for an MCU-internal environment, it is rather mediocre compared to external one's. While adding the cost of an extra chip, it might reduce costs for analogue interfacing circuitry (which you definitely need for the internal DACs), and give you an easy option for more channels.

[sbsohrabi]

Posted on August 22, 2014 at 09:48

Thank you

I had no success.We can not have HS USB and DAC2 in one application.The price of adding an external DAC is high in this application.It seems waste of resources in F4 family of devices.i just don't know about the reason. and why the topic didn't covered anywhere. how can I access the ST support ?

[frankmeyer9]

Posted on August 22, 2014 at 11:21

It seems waste of resources in F4 family of devices.

Might be a use case that ST had not envisioned.how can I access the ST support ? Usually via a local representative or FAE. Or you can try this :

http://www.st.com/stonline/contactus/contacts/index.php?type=2