AM335x Warm Reset Output Falling time

Hi,

I will ask the factory team to comment.

Feedback from the factory team:

This is not what I would expect from AM335x driving the signal.  If AM335x were driving the signal, I would expect the rising edge to have the RC curve and the falling edge to be driven which is opposite of what is shown in the scope shot.  It looks like something else is driving the signal low.  Ask them if something is connected to P2 (JTAG connector).

Hi Biser-san,

Thank you for your reply.

AM335x should be driving low the signal even if something is connected to P2 (JTAG connector) because Warm Reset is triggered by setting RST_GLOBAL_WARM_SW bit in PRM_RSTCTRL Register.

Best regards,

Daisuke

 

The question was: Is something connected to P2 while these diagrams are observed?

Hi Biser-san,

Thank you for your reply.

Nothing is connected to P2 (JTAG connector) and P9 (EXPANSION HEADER).

 

RST_GLOBAL_WARM_SW bit in PRM_RSTCTRL Register is set in the console (u-boot) on BBB.

Best regards,

Daisuke

 

Here is the waveform I would expect to see.  The open-drain output drives the signal low faster than the pullup is able to pull the signal high.

This was captured on the EVM.

It seems like something on the board is loading the nRESETIN_OUT pin. We certainly don't anticipate 100's of ns fall time for this pin since this is an active driver as Paul mentioned.

Can you eliminate the switch and any other connections to this pin (no other load) nRESETIN_OUT and see if you observe the same behavior?

Regards, Siva

Hi Siva-san and Paul-san,

Thank you for your reply.

No. I cannot eliminate the ethernet PHY (LAN8710A).

The nRST pin of LAN8710A should not affect it in particular since the pin is the variable voltage schmitt-triggered input and has 50uA (typical) internal pull-up.

ww1.microchip.com/.../8710a.pdf

Best regards,

Daisuke

 

Hi Paul-san and Siva-san,

On the EVM the nRESETIN_OUT pin does not connect to the ethernet PHY (AR8031_AL1A) directly but connects via the buffer (SN74LVC1G07). I expect that the nRESETIN_OUT output is poor in driving capability.

What is the maximum low-level output current of the nRESETIN_OUT output?

Should a buffer be used for the nRESETIN_OUT output?

Best regards,

Daisuke

 

Daisuke Maeda said:

What is the maximum low-level output current of the nRESETIN_OUT output?

See p.90 of the AM335X Datasheet, Rev. H. Output high/low levels are rated at 4mA current.

Hi Biser-san,

Thank you for your reply.

I have already checked the specification in datasheet. I am concerned that the nRESETIN_OUT output does not meet it.

Best regards,

Daisuke