Wrong Ethernet connection in FRDM-K64F

[etronic_arg]

Hi guys,

I was looking at FRDM K64F schematics from FRDM-K64F-SCH-E4.pdf and it seems to be a mistake in the connection between PHY (U13 KSZ8081RNACA) and RJ-45 Jack (J13).

There is a 0 ohm resistor between TCT and RCT. In fact, I measured the board and there is a short between pin 3 and 6. However, in the phy datasheet says:

(Document DS00002199A-page 45)

"11.0 MAGNETIC - CONNECTION AND SELECTION A 1:1 isolation transformer is required at the line interface. Use one with integrated common-mode chokes for designs exceeding FCC requirements. The KSZ8081RNA/RND design incorporates voltage-mode transmit drivers and on-chip terminations. With the voltage-mode implementation, the transmit drivers supply the common-mode voltages to the two differential pairs. Therefore, the two transformer center tap pins on the KSZ8081RNA/RND side should not be connected to any power supply source on the board; instead, the center tap pins should be separated from one another and connected through separate 0.1 µF common-mode capacitors to ground. Separation is required because the common-mode voltage is different between transmitting and receiving differential pairs."

So, what is the 0 ohm resistor for?

Best wishes,

Pablo

[Jonathan_Iglesias]

Dear Pablo Liberman,

Please check the  DS you sent is not from the manufacturer of the connector of the K64.

please check the BOM, the J13 connector and the manufacturer.

FRDM-K64F Platform|Freedom Development Board|Kinetis MCUs | NXP 

Have a great day !

BR

Jonathan

[etronic_arg]

Dear Jonathan,

Thank you for taking the time to send me your comments.

May be I did not express myself well, but the quoted text comes from U13 (KSZ8081RNACA), not from the connector J13. It doesn't appear in the figure but it is in the same page of FRDM's schematics.

It seems to be a 0 ohm resistor (R83) between pins 3 and 6 of the J13. However the Phy manufacturer states that they should be separated.

Hope it is now clear.

Best wishes,

Pablo

http://ww1.microchip.com/downloads/en/DeviceDoc/KSZ8081RNA_RND.pdf 

[Jonathan_Iglesias]

Dear Pablo Liberman,

based on the bill of materials of the Frdm board, the information about the manufacturer is the following:

 the manufacturer is not the one in the link you sent, therefore their recommendations not necessary apply to this part, this was a change done in 2014 ( adding the resistor).

Have a great day !
Jonathan