DM816x GMII Not Compatible with 2.5V I/O Ethernet PHY

Shareef

Expert 1985 points

Hi,

As I understand, it is possible to interface Ethernet PHY whose I/O supply is 2.5V (like 88E1111) to the GMII interface of DM816x as it meets the electrical specs (Vih and Vil) of Netra at RXD side. The specs are met even if I consider the margins due to power supply noise.

Whereas in TXD side it is fine since the PHY I/Os are 3.3V tolerant.

What I don't understand is that in the DM816x Datasheet it is mentioned that "Only Ethernet PHYs with 3.3V I/Os interface should be used".

Can you please provide me the right reasoning for this?

Regards,
Shareef

over 10 years ago

0 Pavel Botev over 10 years ago

TI__Guru**** 170625 points

Hi Khader,

I found in the below e2e thread that they are able to use Marvell 88e1111 in their DM816x custom board:
e2e.ti.com/.../1144354

See also the below e2e thread:
e2e.ti.com/.../98329

Regards,
Pavel

0 Shareef over 10 years ago in reply to Pavel Botev

Expert 1985 points

Hi Pavel,

I understand that some may have tested it. It will help to get the technical reasoning behind mentioning that "not compatible with 2.5V I/O signalling". While we see that it is possible even considering some power supply noise margin of -5%, Voh = 2.17V (2.37 - 0.2). (Voh of 88E1111 PHY is Vdd - 0.2V), in ideal case Vdd = 2.5V.

Regards,
Shareef

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DM816x GMII Not Compatible with 2.5V I/O Ethernet PHY