Dumping registers on SD clock line of i.MX6 solo EVK

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Dumping registers on SD clock line of i.MX6 solo EVK

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asou_junichi
Contributor I

Hi,

I am looking at the schematic of IMX6SOLOX_SABRESDB-DESIGNFILES then noticed there are 10 Ω dumping resistors on each SD clock lines(R53, R94 and R83).

When R83 on SD4_CLK were replaced with 0 Ω resistor, I obserbed the SD card could not work with SD4 ports.

The below is the picture of SD4_CLK with 0 Ω resistor on i.MX6 side, there is a spike on the rising edge.

clk_mx.png

But the there is no spike on the SD4_CLK on SD card side. (see below)

clk_sd.png

In case of R83 with 33 Ω resistor,  SD card works.

Then I have some questions.

Q1.

What are the purpose of those resistors and why are those needed?

Q2.

Dose the spike on SD4_clock affect the data sampling for receiving data from the SD card?

BR,

JA

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asou_junichi
Contributor I

Hi,

Thank you for answer.

I understood that the ringing on the clock affect the data sampling against the receiving data.

I think that the receiving data is sampled by the clock which is on the clock line.

Regarding the wave form of sending data, the data is correctly syncronized with the clock and the content of command and of data are also correct. It seems that the ringing on the clock does not affect the sending data. I would like to know why the ringing on the clock does not affect the sending data on the data lines.

Q1.Could you tell me which clock source is used to syncronize the data sending?

Is it the clock on the clock line(clock with ringing), the clock without ringing or something else?

BR,

JA

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igorpadykov
NXP Employee
NXP Employee

Hi

>Q1.

one can check sd timings in sect.4.12.5 Ultra High Speed SD/SDIO/MMC Host
Interface (uSDHC) AC Timing i.MX6SX Datasheet (rev.2, 6/2016)
https://www.nxp.com/docs/en/data-sheet/IMX6SXCEC.pdf

Best regards
igor

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igorpadykov
NXP Employee
NXP Employee

Hi 麻生 淳一

>Q1.What are the purpose of those resistors and why are those needed?

they are for improving signal shape, removing ringing.

>Q2.Dose the spike on SD4_clock affect the data sampling for receiving data from the SD card?

yes it can affect. In customer designs recommended to follow sect.3.5.8 High speed

signal routing recommendations IMX6SXHDG Hardware Development Guide for i.MX 6SoloX

http://www.nxp.com/assets/documents/data/en/user-guides/IMX6SXHDG.pdf

Best regards
igor
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