STM32L07x to STM32U083 migration and pincompatibility (AN6091)

Hans_W · ‎2024-08-14

I'm planning to drop in an STM32L083RC into a design made for STM32L071/073/083RZ (LQFP64) and was confident after reading AN6091 that apart from USBVDD it would be pincompatible.

It appears I cheered too soon, after I dived into the U083 datasheet and pin functions: The STM32U0 misses the second MCO output on PB13(pin 34) and the USART on PB3-PB4 (pins 55-56), where the L07x has USART5.

That results in quite a bit more redesigning than only disconnecting the unused USB power.

I guess that the AN6091 document should warn in Table 21 that USART pinout compatibility is partial and in Table 25 that the second MCO output of the L07x is not available on U0 series.

KDJEM.1 · ‎2024-08-19

Hello @Hans_W and welcome to the community 🙂,

The STM32L073 has a four USART (USART1, USART2, USART4 and USART5) as mentioned in the datasheet:

And in AN6091 application note table 21 you can see that the number of USART instances in STM32L0 is up to 4.

I think, the AN6091 is in line with STM32L073 datasheet.

For table 25. is a RCC differences between STM32L0 and STM32U0 series that mean is applicable for all STM32L0 series and for all STM32U0 series.

For example in STM32L063, the MCO is not available in pin PB13 as shown in STM32L063 datasheet.

As table 25. in AN6091 is applicable for all STM32L0, only PA8 is mentioned which is supported by all STM32L0 series.

These FAQs can help you to find the compatible devices for an MCU and to migrate from MCU1 to MCU2:

Please let me know if your request is answered or not?

Thank you.

Kaouthar

To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

Hans_W · ‎2024-08-19

Thank you Kaouthar,

I accidentally clicked on "Accept solution" while trying to uncheck that before clicking Reply.

The issue I have with AN6091 is that i presumes pincompatibility for the USARTs, in the sense that an U0 device with the same or higher number of USARTs as the L0 would likely be pincompatible, which unfortunately it isn't.

Not only USART5 is unavailable in U083 on PB3-4, many more U(S)ARTS cannot be mapped to the same pins, even though U0 has twice the number of Alternate Function settings compared to L0:

PA13-14 and PC10-11 can't be an LPUART in U0 (although U083 has twice the number of LPUARTS compared to L0)

PA14-15 can't be a USART in U0 (missing TX)

PB10-11 can't be TX/RX of LPUART1 in U0 (only RX/TX, swapping not possible like in L0), but you can use a different USART (3) there.

That is only the incompatibilities on RX/TX and there may be a few more.

So there are many incompatibilities when migrating from the most complete L0 to the most complete U0 MCU, it would seem a good idea to point that out for those planning to migrate from L073/L083 to U073/U083, especially because those type numbers are very alike you would think that if AN6091 states pincompatibility that it would definately apply to thise cases.

KDJEM.1 · ‎2024-08-28

Hello @Hans_W ,

Thank you for this explanation.

I confirm the USART pinout compatibility issue.

I reported this issue and your idea internally.

Internal ticket number: 189719 (This is an internal tracking number and is not accessible or usable by customers).

Thank you.

Kaouthar

To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

Viktor POHORELY · ‎2024-08-29

Thank you for those detailed points. AN will be updated with such warning.