Connections between Ethernet PHY and Switch

[FreshmanNewbie]

I am having this Ethernet PHY - LAN8840 and this Ethernet Switch - KSZ9567

I want to use RGMII interface between them. Port 6 of KSZ9567 is RGMII between KSZ9567 and LAN8840.

So, I want to know how to connect the Tx and Rx of the devices in this interface.

Since, for RGMII, there's no concept of MAC and PHY, since RGMII is Source synchronous interface, I am confused.

I checked in the HW Checklists of both the device. Links: KSZ9567 and LAN8840.

On the figure on Page 10 of the LAN8840 checklist, the connections between the LAN8840 PHY and MAC device is Tx to Tx and Rx to Rx.

Whereas, on page 19, Figure 8.4 on the KSZ9567 checklist, the connections between the KSZ9567 and LAN8840 (PHY pin definition - I took this figure because LAN8840 is a PHY), is Tx to Rx.

Both seem to conflict. Can someone tell me which is the correct method of wiring the Tx and Rx between the devices?

Also, When you see the pin buffer type of RX pins of both the devices, they seem to indicate that Rx pins are output pins and have output buffers in both the devices.
So, shouldn't it be Tx to Rx connections between the LAN8840 and the KSZ9567 devices?


Going through this Eval board's RGMII interface - KSZ9477, It is wired Tx to Tx and Rx to Rx.

Totally confused. Can someone clarify?

 

[FvM]

You need to check individual datasheets, they clearly what's in- or output. Application examples can be wrong.
As far as I understand, SGMII Rx/TX notation for MAC/PHY combination is reflecting the MAC perspective. Respectively the names of PHY components as LAN8840 are reversed, Rx is connected with Rx and Tx with Tx. In MAC/MAC combination they should be crossed. The Evalboard schematic looks wrong, KSZ9477 and ARM processor expose both MAC interfaces.

 

[FreshmanNewbie]

You need to check individual datasheets, they clearly what's in- or output. Application examples can be wrong.
As far as I understand, SGMII Rx/TX notation for MAC/PHY combination is reflecting the MAC perspective. Respectively the names of PHY components as LAN8840 are reversed, Rx is connected with Rx and Tx with Tx. In MAC/MAC combination they should be crossed. The Evalboard schematic looks wrong, KSZ9477 and ARM processor expose both MAC interfaces.

Thank you.

So, with my KSZ9567 and LAN8840 RGMII, I need to connect Tx to Rx only, right?

 

[FvM]

If you refer to pin names, no. Always connect output to input pin. On LAN8840, input pins are named TxD and output pins RxD, as explained above.

 

[FreshmanNewbie]

If you refer to pin names, no. Always connect output to input pin. On LAN8840, input pins are named TxD and output pins RxD, as explained above.

I am confused. Can you tell me whether this connection is correct?

 

[FvM]

Yes correct.
KSZ9567 symbol has incorrect signal directions. TXxx pins are outputs but have an input arrow. Also placement of series resistors at the MAC side is questionable, they should be placed at output pins (source side serial termination).

 

[FreshmanNewbie]

Yes correct.
KSZ9567 symbol has incorrect signal directions. TXxx pins are outputs but have an input arrow. Also placement of series resistors at the MAC side is questionable, they should be placed at output pins (source side serial termination).

Oh thanks.

1. When you mention TXxx pins are output but have an input arrow, you mean the black arrow, right?

2. Also, Rx pins of KSZ9567 is connected to Rx pins of LAN8840. But in the datasheet of both devices, Rx pins are mentioned as output.

LAN8840 datasheet:

KSZ9567 Datasheet:

But you mentioned, always connected Outputs to Inputs.

So, as per the schematic I shared above, Tx pins are connected to Tx. And Rx pins of the devices are connected to Rx.
So, output pins are connected to output pins. Which is incorrrect, right? Confused again, sorry.

Please clarify.