topic Re: Why doesn't NXP use termination resistors for MII data lines? in i.MX Processors

Why doesn't NXP use termination resistors for MII data lines?

triedgetech — Mon, 25 Oct 2021 12:53:26 GMT

In i.MX 8M Mini EVKB base board there are no termination resistors for its ethernet interface.

Schematic can be obtained here.Under "i.MX 8M Mini LPDDR4 EVKB Base Board Design Files".

There should be termination resistors for MII data lines (ENET_TD0, ENET_TD1... ENET_ RD0, ENET_RD1...), but there isn't, why?

It's common knowledge, termination resistors for transmission and receive data lines between PHY and MAC are needed to avoid high-speed signal reflections, it's part of impedance matching technique.

Manufacturer of PHY ICs called Microchip says so here on p. 20.

Altium also has an article on it:

"Designers should check the PHY and MAC datasheet for the presence of internal termination resistors, and if they do not exist, they must be placed on-board." (c)

Why didn't NXP use termination resistors between AR8031 PHY IC and CPU i.imx8m mini? Am I missing something here?

Re: Why doesn't NXP use termination resistors for MII data lines?

triedgetech — Thu, 28 Oct 2021 05:11:52 GMT

Any EE engineers from NXP browse this forum?

Re: Why doesn't NXP use termination resistors for MII data lines?

BiyongSUN — Sun, 31 Oct 2021 09:15:57 GMT

We respect the common knowledge in IEEE spec. not others' articles.

In the spec, only says the impedance not a certain terminal resistors.

BTW, in IEEE spec, it also respects to the spec ISO 11801.

several ways to achieve the impedance.

"it's part of impedance matching technique." --- only put terminal resistors can do the matching?

It is one of impedance matching technique. not "part of".

In the i.MX8MM hardware design guide, already mention the layout impedance. read the hardware design guide and finish your own design.

Copy some in IEEE spec. and please read the IEEE spec carefully. and found what you need.

and do not quote any articles but spec.

If you still have questions, please quote IEEE spec and say it is wrong. and we will check it.

please read IEEE spec. and others' articles could be under their certain context.

Manufacturer of PHY ICs called Microchip says so here on p. 20.

Altium also has an article on it:

"Designers should check the PHY and MAC datasheet for the presence of internal termination resistors, and if they do not exist, they must be placed on-board." (c)"

that you quote above is their case, and they also refer to their ''design.

and the authors of those articles/document, they never say it is common knowledge. they said "Designers should check "

Where is the "common knowledge" you mentioned, please show the spec.

Just i.MX8MM don't need termination resistors for MII data lines is very equal to in the article need termination resistors.

But they all respect IEEE spec.

Re: Why doesn't NXP use termination resistors for MII data lines?

BiyongSUN — Sun, 31 Oct 2021 11:24:09 GMT

EE engineers? What is EE engnieers?

Is it a "common" title all around the world?