DP83822H: DP83822 + ET1100 for EtherCAT application issue

Hello,

Odd nibble detection is a functionality where the PHY will recognize an appended packet (error packet according to EtherCAT) as a faulty packet. Disabling this will allow compatibility with the EtherCAT topology which utilizes appended nibbles to determine errors on the bus.

Sincerely,

Gerome

Hi Gerome, 

1. Where's Odd nibble detection happen? At MII side while receiving data, or at RJ45 side while receiving data? Do you have a block diagram or something to demonstrate?

2. When odd nibble detected, what would be DP83822 behavior?

3. Do we have odd nibble detection disable EtherCAT solution?

Hello,

When a corrupted packet is detected by the MAC one port, when forwarding to another port, it will append a nibble to the packet to indicate there is an error instead of throwing the packet away. This is critical for EtherCAT topology for system users to identify where is the corruption in a long daisy chain occuring by indicating if a received packet has an error or a forwarded error to help track down the weakness in the chain.

DP83822 has Odd Nibble enabled by default, but has register configuration available to disable. DP83826A has this feature available to disable via strapping when in Enhanced Mode.

Sincerely,

Gerome

Gerome Cacho said:

DP83822 has Odd Nibble enabled by default, but has register configuration available to disable. DP83826A has this feature available to disable via strapping when in Enhanced Mode.

Hi Gerome, 

WIll DP83826A P2P with DP83822?

Customer wants to disable the "odd nibble detection" without PCB change. 

Thanks a lot!

Hi Sean,

DP83826A is not P2P with DP83822. If customer wants to hardware change to DP83826A, they will need to slightly redesign their layout. 

Sincerely,

Gerome

Hi Gerome, 

Can we use tool "USB-2-MDIO" to write register of DP83822 to disable odd nibble detection?

https://www.ti.com/tool/zh-tw/USB-2-MDIO

Pls kindly suggest, thanks a lot!