AM6442: Meaning of resistance value between AM64 and FPGA.

Hi Ito-san,

It does not make much sense.Series term resistors are usually placed near the output buffer, and sized to bring output impedance up to match PCB trace impedance.

AM64x output impedance is ~50R and does not need a series resistor to match a 50R trace impedance.

Are the data outputs only to FPGA? Is there another pull-down resistor shown below the screenshot - maybe forming a resistor divider?

 - without pull-down, the 820 might make the edge rate slower (RC time constant). Voltage may be between VIL and VIH too long with slow edge rate.

 - with a resistor divider, the current draw may be too high for the IO buffer

Regards,
Mark

Hello Ito,

Thank you.

If you can share the complete implementation of the bootmode configuration, i can add additional comments.

The below FAQ can be referenced for bootmode implementation.

Bootmode buffer boot mode buffer
e2e.ti.com/.../faq-am625-am623-am644x-am243x-am62a-am62p-am62d-q1-am62l---bootmode-implementation-without-buffers
https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1414148/faq-am625-am623-am644x-am243x-am62a-am62p-am62d-q1-am62l---bootmode-implementation-with-buffers

EVM / SK implements bootmode with buffers. 

Regards,

Sreenivasa