DP83826E: Typical application guide with Strap configurations at RMII Master Basic mode

ArTzy

Part Number: DP83826E

Hi Experts,

Seeking your guidance on this query I am posting on behalf of my customer.

Initially, they are asking the reference design for DP83826ERHBR, as they wanted to know how to design STRAPS pins for RMII Master Basic mode, with the LED0/1 pins. Referred them to its EVM references.

Now, they would also like to know all Straps configuration externally with resistors.

For example, in the Table 7-1 of the datasheet of the DP83826ERHBR stands for the strap4 (pin name COL) that the strap is not used in RMII mode, but in section 9.4.1.2 in the strap configuration for Basic mode we need to pull the pin up to high for RMII master mode.

For strap1, according to table 9.4.1.2 as well a pull up to high for Speed 100M is needed but with your description its pulled down go GND.

Could you give me some advise about the other Straps at RMII Master Basic mode?

Regards,
Archie A.

www.ti.com/.../snla338a.pdf

over 2 years ago

0 David Creger over 2 years ago

TI__Mastermind 26712 points

Hi Archie,

The COL signalling pin is not used in active RMII mode, but the pin is still used as a bootstrap upon power up.

Section 9.4.1 of the datasheet explains how to use the hardware bootstraps. Section 9.3.17 explains how to bootstrap the LED pins.

Thanks,

David

0 ArTzy over 2 years ago in reply to David Creger

TI__Genius 17415 points

Hello David,

Thank you.

We are not sure how our design has to be with the straps.

Strap0 is on the same pin like RX_D0. But it is not clear to me how I can use the RX_D0 connected to my processor but at the same time it has to be pulled high. Does that work if I just pull-up the pin to high, but it works as well for the communication to the processor?

73,
Archie A.

0 David Creger over 2 years ago in reply to ArTzy

TI__Mastermind 26712 points

Hi Archie,

Please see the following video on ethernet bootstraps. This will give you a good idea how straps work. https://www.youtube.com/watch?v=pvfJk-LJ7Yo

Thanks,

David

0 ArTzy over 2 years ago in reply to David Creger

TI__Genius 17415 points

Thanks, David.

Yes it helps, but my question is still not answered.
What if I has to Pull-up or Pull-down the RX_D0 pin, if its used for communication with the Mac? How does the schematic looks like?

In the video you send me, there was like 2 times the RX_D0 pin on the phy, one was pulled up, the other normally connected to the Mac. So?

Regards,
Archie A.

0 David Creger over 2 years ago in reply to ArTzy

TI__Mastermind 26712 points

Hi Archie,

Strap pins are dual functionality. The pins are used for strapping as well as communication with the mac. The strap does not affect communication. The pull up or pull down resistor is weak enough that the PHY can still drive the pin to the desired voltage level.

Thanks,

David

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DP83826E: Typical application guide with Strap configurations at RMII Master Basic mode