DP83848 Tx not working

[ingdb]

Hi all,

we have a custom board with STM32H753 MCU and a DP83848 PHY. When configuring the PHY in loopback mode I can send and receive messages as expected. But when not in loopback mode we can receive data but the Tx path is not working.

As the loopback mode is working and it's happening on every instance of the board the problem should be related to the connection between DP83848 and the 74990101210 RJ45 LAN transformer, but we're not seeing anything odd. 

 

Does anyone sees a problem in this schematic?

best regards

Matthias

 

 

[LCE]

Looks good to me.

Checked the termination resistors (R61, R62)?

Checked the PCB?

Any registers in the PHY to activate TX?

[ingdb]

all registers are configured as it should be. For a test I coupled a STM32F7 eval board (with working Ethernet) and my custom board. The data transmitted from the custom board is not received on the eval board, nothing new here. But the weird thing is, when I sent a frame from the custom board the LED of the STM32F7 eval board is blinking. So it looks as if the PHY sees data but it's not transmitted to the MCU.

[LCE]

> the LED of the STM32F7 

Ah, this one... ;) Do you mean one of the RJ45 connector LEDs ?

So it looks like the H7 is sending something.

Have you connected the H7 board to a PC and checked traffic with Wireshark?

[ingdb]

yes, that's how I started, No Tx data from my custom board. When connecting my board to the Stm32F6 eval board still no data received but on the Eval board at least the green LED is blinking accordingly to the data rate I am sending from the H7.

=> The PHY sees enough to toggle the LED but no data transmitted to the Ethernet driver on Stm32F6 eval board. The software/hardware on the Stm32F6 eval board can't be an issue as ethernet on this board is working as expected.

[LCE]

So the H7 is probably sending something, but crappy data, which might be the slightest error in the header or so.

-> Wireshark might help

[ingdb]

as I said, nothing received on Wireshark