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Isolation resistors for Bootmode pins on the AM62A Mity-SoM?

Added by Leonardo Marquez 2 months ago

Hi,

On the TI's Eval board for the AM62A (AM62A-SKEVM) they include isolation resistors between Bootmode signals and the SoC pin as shown:

AM62A-SKEVM resistors

However, on Critical Link's Devkit those resistors don't exist:

Critical Link Boot mode sch

Are those resistors on the MitySOM instead, or simply they are not needed?


Replies (5)

RE: Isolation resistors for Bootmode pins on the AM62A Mity-SoM? - Added by Leonardo Marquez 2 months ago

Also, anyone knows how to insert the images in line with the text instead of as an attachment at the end of the post?

I'm new to this forum, sorry about that.

RE: Isolation resistors for Bootmode pins on the AM62A Mity-SoM? - Added by Jonathan Cormier 2 months ago

Also, anyone knows how to insert the images in line with the text instead of as an attachment at the end of the post?

There is an image button that helps with this. I edited your post for readability.

Are those resistors on the MitySOM instead, or simply they are not needed?

Since the devkit uses those pins for video out, the boot config pull-downs/ups are unlikely to affect the HDMI chip and vice versa. If you plan to use the pins for other uses, it is a good idea to ensure the functions don't interfere with the boot mode latching and visa versa.

Feel free to share your schematic with , and we will happily do a schematic review.

RE: Isolation resistors for Bootmode pins on the AM62A Mity-SoM? - Added by Leonardo Marquez 2 months ago

Thanks Jonathan.

I plan to use those video out signals to drive a parallel RGB 24-bit display instead of an HDMI chip. I am considering adding the isolation resistors but make them 0-ohm initially, just to be safe. This way they can be changed to a different value in case the there are issues with the bootmode latching.

RE: Isolation resistors for Bootmode pins on the AM62A Mity-SoM? - Added by Michael Williamson 2 months ago

Hello,

For the bootmode pins:

1. If you are concerned about isolation, you can use a tristate buffer to drive/tristate the bootmode pins using the PORz_OUT signal from the SOM. See the schematic below as an example we used for another carrier card for the SOM instead of inline pullup / pulldown resistors.

Note that R200 R202 and R203 should not be fitted.

2. Bootmode pins 2:0 are pulled up or down on the SOM.

3. Make sure you are pulling them to the VDDSHV3 rail (in case you are not using 3.3V).

Thanks!
Mike

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