UART Communication Directly Between Two S32K1xx MCUs

[hongpingxu-b364]

Hi,

My customer use two S32K1xx MCU on one board, and connect directly with UART.

Customer found that UART communication will be failed if no external pull-up. Customer wonder whether the external pull-up is mandatory 佛如direct connection application?

BR,

Hornby

[hongpingxu-b364]

Hi Robin,

Thanks for your reply.

Customer used S32K144 and S32K116 with last Maskset, and only configured MUX bitfield on PORT_PCRn register. Just add external pull-up resistor to make UART communication normal.

These two S32K1xx chips are powered on the same supply. The first UART message send around 2s after power on, so customer make sure that these two S32K1xx MCU are finished initialization already.

We also push them to enable internal pull-up, but customer wonder 1.) why old solution with STM32 and same configure can work properly; 2.) S32K1 internal pull-up/down are weak pull, customer oppugned the communication  reliability.

Best regards,

Hornby

[Robin_Shen]

I don't have S32K144EVB on hand, so just test it on S32K146EVB and S32K116EVB. Modify the lpuart_echo example in S32K1xx SDK RTM v4.0.2, change the pins in order to connect directly. 

S32K146EVB   default      modified
LPUART1_TX   PTC7       PTC9   J6 16
LPUART1_RX   PTC6       PTC8   J6 13

S32K116EVB    default      modified
LPUART0_TX   PTB1        PTA3   J1 2
LPUART0_RX   PTB0        PTA2   J1 1

It was able to communicate normally. So would you please let customer check their circuit?(common ground?)

These pins only configured MUX bitfield on PORT_PCRn register. Did not enable the internal pull-up resistor.

[Robin_Shen]

Hi Hornby,

Whether the customer's application software these two cases:

Just add external pull-up resistor to make UART communication normal?

What value is set in the PORT_PCRn register of the LPUART_RX pin? 

If the internal pull-up resistor is enabled, is it possible to have the same phenomenon as using an external pull-up resistor?

Are two S32K1xx chips powered on at the same time? Is one of the chips not working at all, or is it just the LPUART communication part that is not working?

Please tell me the part number and mask set of two S32K1xx. 

Best Regards,
Robin
-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!

- We are following threads for 7 weeks after the last post, later replies are ignored
Please open a new thread and refer to the closed one, if you have a related question at a later point in time.
-------------------------------------------------------------------------------