about pin mode during POR on i.MX6ULL

[george]

Hi all,

In our schematics, the UART3_TX_DATA pin connects to the LED access indicator.
The LED access indicator should not turn on because the UART3_TX_DATA pin should be in input mode during POR.
However, for some reason the LED turns on during POR.

We found the hint in the UL datasheet.

    

Does this also apply to ULL?

If so, why isn't it shown in the ULL datasheet?

BR,

George

[Yuri · Accepted solution]

@george 
Hello,

  According to section 32.6.25 [SW_MUX_CTL_PAD_UART3_TX_DATA SW MUX Control
Register (IOMUXC_SW_MUX_CTL_PAD_UART3_TX_DATA)] of i.MX 6ULL  Reference Manual
(Rev. 1, 11/2017): 
   ALT7 mode will be automatically active (output SJC.SJC_JTAG_ACT) when system
reset. Once system reset is completed, the state of UART3_TX_DATA will be output
keeper and input enable.

Regards,
Yuri.

[george]

Dear @Yuri,

As you say we could find a description about it in the reference manual.

Thanks,

George

[mrudang_shelat]

@george ,

From which part datasheet you received Table 96?

In i.MX6ULL, UART3_TX_DATA pin is the default GPIO configured (ALT5: GPIO1_IO24) as an Input. So It should not have an output blink for LED unless the functionality of pin configuration changes.

You can refer section 32.6.25: SW_MUX_CTL_PAD_UART3_TX_DATA SW MUX Control Register of the iMX6ULL Reference manual.

Mrudang

[george]

Dear @mrudang_shelat,

Thank you for your response.

Our LED indicator is Low-Active.

Now we use the UART3_TX_DATA pin with an external pull-up.

It seems that the UART3_TX_DATA pin is driven low after 20mS after POR_B is asserted and after that until POR_B is deasserted.

During that time, the LED turns on.

This is consistent with the behavior described in the UL datasheet

BR,

George