DP83TG720S-Q1: DP83TG720S-Q1 CRC errors

Hello Peppe, 

Thank you for the message.

Could you please help me with some additional details.  Are you doing some testing and facing some issues. If yes please provide some additional details.

These bits cover the DAC current and hence the swing.

Regards,

Sreenivasa

Hello

I am doing some tests and in some cases I see CRC errors.

Is there any tuning expected for the register mentioned ? The description is not so clear for me.

many thx

peppe

Hello Peppe,

Thank you for the inputs.

The registers you mentioned are for the MDI interface.

Can you please provide more details on what board you are using, what is the setup and the tests you are performing.

Regards,

Sreenivasa

hi Sreenivasa

the test is very simple, the MAC generates UDP datagrams, these are sent PHY via SGMII. The PHY is programmed in loopback mode.

I tested different loopback modes: Digital, Analog, SGMII and I get always same behavior.

I want to understand if there are SGMII registers that can be used for understanding if the interface has problems or the PHY needs to be programmed in some way. 

Regards

peppe

Hello Peppe, 

Thank you. 

Are you using an EVM or a custom board. Are all the required terminations in place?

Regards,

Sreenivasa

Hello Sreenivasa

I confirm, I am using a custom board, where the mac is attached to the PHY via SGMII and there are only the capacitors as recommended in the documentation:

I am programming the PHY in loopback as said in my previous comment.

Which terminations I should adopt?

regards

peppe 

Hello Peppe, 

Thank you for the inputs. 

I assume you have followed 

Table 7-2. Datapath BIST Programming

You mentioned you are seeing some CRC errors - do you have some additional details on the count.

Is the MAC and the phy voltage levels verified.

Regards,

Sreenivasa

Hello Sreenivasa

I found the root cause of the CRC failures and this is due to the capacitors below that have to be removed from my PCB. Please can you detail me why they should be placed on? 

regards

peppe

Hello Peppe, 

Thank you for updating. Is the MAC an FPGA  ?

Regards,

Sreenivasa

Hello 

this is a MAC not in an FPGA

I have the following two questions too:

1. The transceiver doesn’t report any indication about the specific type of these capacitors. Please can you give me more indications about which capacitor embedded on the PCB?
2. I wonder if the transceiver can work w/o any capacitors on these signals.

regards

peppe

Hello Peppe,

Please refer to the application section of the datasheet for the capacitor recommendations.

8.1 Application Information

The EVM would provide the details that you are looking for.

this is a MAC not in an FPGA - Can you please elongate what you meant by MAC.?

Regards,

Sreenivasa

Hello

We refer to 8.1 Application Information

removing the capacitors the SW doesn't detect any error. With the capacitors after a while the CRC errors are detected by the Ethernet.

> The EVM would provide the details that you are looking for.

Can you share me the link of the EVM to check the HW? Really apretiate.

> this is a MAC not in an FPGA - Can you please elongate what you meant by MAC.?

Sure, our MCU has own Ethernet controller wired in SGMII mode to the TI transceiver (like the picture above).

Regards

Peppe

Hello Peppe, 

Thank you for sharing the info.

Please see below.

Regards,

Sreenivasa

Hello Peppe, 

Please let me know if you have additional questions. If not please let mw know if i can close he thread.

Regards,

Sreenivasa

Hi Sreenivasa

below there is device spec and, per this spec the receiver path is AC coupled.

Note that when I remove the coupling capacitors there are errors.

I have the following three questions:

1. whether you can share the values of driver offset-voltage/common-mode voltage. Both min and max values.
2. what does it mean the ROUT-DIFF in the above table? Is it the termination required on the RX side?
3. What does it mean the RIN-DIFF in the below table? Is the termination resistor integrated inside the PHY?

Best Regards

peppe

Hello Peppe, 

Previously the understanding was that the errors were seen with the caps  but in the last message you say when you remove tee caps there are errors. Can you please confirm the right configuration.

Regards,

Sreenivasa

Hi Sreenivasa

with capacitors -> errors

w/o capacitors -> no errors

Please can you reply , my previous questions? These are very urgent.

Many thx in advance

regards

peppe

my fault: Note that when I remove the coupling capacitors there are _NO_ errors.

Hello Peppe, 

Thank you for clarifying.

We do not recommend any external termination in the datasheet. The data sheet provides the details for the  termination i and i do not have any additional info to add.

We recommend AC coupling capacitors..

Thanks

Sreenivasa

Hello Peppe, 

Thanks.

Regards,

Sreenivasa

Hello Sreenivasa.

So you don't have any other to share about the meaning of ROUT-DIFF/ RIN-DIFF, but I understand that it is not necessary to have any termination resistors, don't I?

1. whether you can share the values of driver offset-voltage/common-mode voltage. Both min and max values.
2. what does it mean the ROUT-DIFF in the above table? Is it the termination required on the RX side?
3. What does it mean the RIN-DIFF in the below table? Is the termination resistor integrated inside the PHY?

I wonder if  you can confirm that the PHY can work w/o capacitors. Is there any risk?

Many thx for your support, really appreciate.

Regards

peppe

Hello Peppe, 

Thank you for the message.

As i mentioned we recommend AC coupling. Some of the Host interface work without AC coupling and it depends on the design. 

The datasheet does not specify any terminations on the TX or RX.

The SGMII driver specs are provided in the datasheet and we are following the SGMII specifications.

If you need additional inputs on the specs that are not part of he data sheet we will have to connect over private chat, understand the use case and take it forward.

Is the MAC interfaced you are using following SGMII specifications. Can you please share the specifications for he MAC interface you are using. Does the MAC interface specify terminations or AC coupling?

Can you please share the actual board schematics  to review.

Regards,

Sreenivasa

Hi Sreenivasa

before going to other private chat, from the following document, I cannot see any capacitor on differential signals (page 11). And I see the resistors on RX+-.

https://www.ti.com/lit/ug/snlu289/snlu289.pdf?ts=1634040352045&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FDP83TG720EVM-MC

is this evaluation board ok for the PHY DP83TG720S-Q1?

please can you give me more details about that?

regards

peppe

Hello Peppe, 

Please note that the  EVM uses RGMII interface as below.

Could you please provide the below inputs 

Is the MAC interfaced you are using following SGMII specifications. Can you please share the specifications for he MAC interface you are using. Does the MAC interface specify terminations or AC coupling?

Can you please share the actual board schematics  to review.

Regards,

Sreenivasa

Hi Sreenivasa

> Is the MAC interfaced you are using following SGMII specifications. Can you please share the specifications for he MAC interface you are using. Does the MAC interface specify terminations or AC coupling?

Please refer to the chart below to get out specifications compared with yours:

I also understand that the TI PHY does not have capability to change the SGMII output strength.

I had asked for more details about that:

Regards

Peppe

Hello Peppe, 

Thank you for the info.

The register is for the MDI line driver.

Regards,

Sreenivasa

so there is no way to change the SGMII output strength.

Hello Peppe. 

Thank you for the message and  based on the available information in the data sheet  you are understanding is correct.

Regards,

Sreenivasa