DP83867IS: About the relationship between the setting value of the IO_IMPEDANCE_CTRL register and the characteristic change

Hi,

The IO_IMPEDENCE_CTRL register is used to control the impedance on MAC IOs only. For example RGMII, this can effect the throughput i.e the RGMII timings.

For extended register space, we would recommend to follow the MMD read/write operation as mentioned in the datasheet with out any other steps in between.

Regards,
Rahul

Hi Rahul san

I already understand the content of your reply.

Will the impedance characteristics be as follows?
<IO_IMPEDANCE_CTRL register>
0x1F:35ohm, 0x13:50ohm, 0x00:75ohm

I want to know the change in electrical characteristics when changing 1 bit.

I would like to know the answers to the following questions.
> When I check the register value of the IC I have at hand,
>
> The register value seems high, but is it like this?
> Each IC has a different register value, is it adjusted during production?
> What is the range of register values that are adjusted during manufacturing?

Regards,
N.H.

Hi N.H,

Parts shipped will be trimmed 50 ohms .

You can read the value and move the step size down by 2 or 3 to match your pcb value instead of hardcoding to particular value.

Regards,

Rahul

Hi Rahul san

Please tell me the range of trimming when shipped.
I want to know the fluctuation range.

And, 
I want a specific answer to my previous questions.
I'm waiting for the answer.

Regards,
N.H.

Hi Rahul san

Thank you for your answer.

Based on your response, I'm thinking of reading the default value of IO_IMPEDANCE_CTRL register and applying an impedance adjustment to that value.
If the default value of IO_IMPEDANCE_CTRL is 0x0E and you want to reduce the impedance by 3 Steps, change the register value to 0x11.
It is not appropriate to make the changed register value a fixed value.

> Default is set to 50 Ω by trim.
> But the default register value can vary by process. Non default values of MAC I/O impedance can be used based on trace impedance.
What is the range of default values that are trimmed?

> Range and Step size will vary with process. 
I want to know the variation range and/or accuracy.
Could you disclose it?

Regards,
N.H.

Hi Rahul san

I change the question.

By IC design, is the 50 ohm register center value 0x 11, 0x12 correct?
When trimmed, does the register value tend to be larger? Or does it tend to be smaller?
As far as we can see, we have confirmed that the default values are 0x0F, 0x0E and 0x0D.

Please tell me the inspection standard of the trimmed register value in the inspection process at the time of manufacture.
We want to know the range of trimmed register values and determine if we can secure a margin when changing register values.
For example, if you increase the register value by 9 steps to match the impedance to 40ohms,
the added register value will exceed the upper limit if the default value is 0x17.
I want to make sure that doesn't happen.

Regards,
N.Hanamoto

Hi Hanamoto-san,

Is customer designing a board without 50 ohm trace impedance in their production ? What is the reason for this approach ?

As mentioned before Default is set to 50 Ω by trim. But the default register value can vary by process.

We do not have the data or the range of the register values as you have requested.

Regards,
Rahul