i.MX 8QuadMax USB_SS3_TCx reset state

[peterlischer]

According to the Reference Manual (Rev. F), the reset state for the USB_SS3_TCx signals (USB_SS3_TC0, USB_SS3_TC1, USB_SS3_TC2, and USB_SS3_TC3) is 

• mux_mode: DMA_I2C1_SCL or DMA_12C1_SDA
• PULL: pull-down
• DSE: drive 2mA

However, when I measure the four pins, all of them are having a high voltage level when the POR_B signal is held low while all the boot power rails are enabled. Interestingly, it is not driven very strongly high. We have an external 100k pull-down on one of the pins. With this pull-down, I measure 2.94V at the pin. If I change this pull-down to 10k, I measure 0.68V, and with a 1k resistor, I measure 60uV. If I short the pin with my DVM, I measure a current of 70uA. 

Why are these pins high in reset, even though it should have an internal pull-down enabled by default? We are using two of these pins for enabling the output power of USB ports (CONN_USB_OTG1_PWR and CONN_USB_OTG2_PWR). Since the pins are driven high during reset, the USB output power gets enabled for about 1 second during the boot process. 

[igorpadykov]

Hi peterlischer

>Why are these pins high in reset, even though it should have an internal pull-down enabled by default?

by default they are high as described in Table 127. 29 × 29 mm functional contact assignments

column "Reset Condition", "State"  - "PU"

i.MX 8QuadMax Automotive and Infotainment Applications Processors

Best regards
igor

[peterlischer]

@igorpadykov 

Thank you for the very quick answer. I was actually not looking into the reset states listed in the datasheet. I was using only the states in the reference manual and an Excel table we got a long time ago (Pinout_MX8QM.v0.72.xlsx). The information in the table and the reference manual were corresponding. Therefore, we have based our design on this information. 

I compared now the information in the datasheet with the ones I have in the Excel list. I was shocked how many pins have a different reset state. Why are there different information available? Do I need to trust the values in the datasheet or in the reference manual? Does this have anything to do with the SCU doing configurations at boot up? What do the reset values mean in the reference manual if in reality the pins behave completely different?

[igorpadykov · Accepted solution]

Hi peterlischer

it is necessary to trust the values in the datasheet, as Reference Manual gives just

IOMUX module description, while SCU reconfigures pins at boot up.

Best regards
igor