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AM3356: MMC0 4 Bit mode SD Card interface Routing and Layout recommendations

Akshay V
Prodigy 70 points

Part Number: AM3356

Hi,

Planning to use the MMC0 interface of AM3356 for SD Card interface to the processor.

Checked the datasheet and there was no detail on the Layout and Routing recommendations for SD Interface.

Planning to use the below Pins from Processor to connect a uSD interface.

What all are the points to be taken care of on the Design stage and please share the recommended layout guidelines to match the processor requirements.

Also, Please suggest if anything is to be done carefully while doing the design/Layout.

The current allocation from Processor perspective is given below:

Pin 
No 

MMC Signals 

G15 

MMC0_DAT1 

F18 

MMC0_DAT2 

F17 

MMC0_DAT3 

G16 

MMC0_DAT0 

G17 

MMC0_CLK 

G18 

MMC0_CMD 

A13

MMC0_SDCD 

---

Thanks & Regards,

Akshay V

  • 0
    TI__Guru**** 227565 points

    Hello Akshay V

    Thank you for the note.

    Can you please point to the EVM or design that you are referring for me to provide my inputs.

    Regards,

    Sreenivasa

  • 0 in reply to Kallikuppa Sreenivasa
    Prodigy 70 points

    Hi Sreenivasa,

    Was referring to the Beagle Bone Board for micro SDCard Design.

  • 0 in reply to Akshay V
    TI__Guru**** 227565 points

    Hello Akshay V

    Thank you for the inputs.

    II assume you are following the below implementation

    Please provision for protection and also a part to connect the shield and ground.

    Please follow the standard routing guidelines including routing the data and clock as 50R impedance lines, matching the traces and spacing other signal away from other data lines.

    Regards,

    Sreenivasa

  • 0 in reply to Kallikuppa Sreenivasa
    Prodigy 70 points

    Hi Srinivasa,

    Thanks for the points.

    Regarding the SD_CLK, CMD, DAT lines, whether is there any length requirement to be met in design.

    Was checking whether any buffer ICs are required to extend the drive capability from AM335x.

    Also, have you got any idea on how will be the SD_CLK derived from the AM335x.

    Which clock will be used and what will be the dividers used for setting the clock speed.

    What is the maximum clock speed and setting available from AM3356 for uSD Card interface for 4 bit mode.

    ---

    Thanks & Regards,

    Akshay V

  • 0 in reply to Akshay V
    TI__Guru**** 227565 points

    Hello Akshay

    Thank you for the note.

    Akshay V said:

    Also, have you got any idea on how will be the SD_CLK derived from the AM335x.

    Which clock will be used and what will be the dividers used for setting the clock speed.

    What is the maximum clock speed and setting available from AM3356 for uSD Card interface for 4 bit mode.

    Any thoughts of the development environment you are using ? Please open a separate thread for questions regarding the device configurations.

    Regarding the SD_CLK, CMD, DAT lines, whether is there any length requirement to be met in design.

    As a good practice, the CMD and DAT pins are tightly matched may be 100mils.

    The CMD and DAT length should be less than the clock and match to 200mils 

    Which mode do you plan to use?

    STANDARD MODE or HIGH-SPEED MODE

    Regards,

    Sreenivasa

  • 0 in reply to Kallikuppa Sreenivasa
    Prodigy 70 points

    Hi Sreenivasa,

    We are using Linux kernal for the development.

    Will share the query in a seperate thread for this.

    Regarding the length matching the points you mentioned are appreciated.

    The thing we are looking for is whether is there any particular length to which the clock or other MMC0 signals can be drawn..?

    In some other device it was shown as 1000 mils.

    Is there any length limitation for SD_CLK or other SD signals from AM335x..?

    we are planning to use the SD Card in Highspeed mode.

    Whether the AM3356 processor supports this speed..?

    What type of SD Cards(UHS-1..etc.) can be used along with the MMC0 of AM3356..?

    ---

    Thanks & Regards,

    Akshay V

  • 0 in reply to Akshay V
    TI__Guru**** 227565 points

    Hello Akshay,

    Thank you for the note.

    Akshay V said:

    The thing we are looking for is whether is there any particular length to which the clock or other MMC0 signals can be drawn..?

    In some other device it was shown as 1000 mils.

    Is there any length limitation for SD_CLK or other SD signals from AM335x..?

    As a thumb rule 500 mils to 2000 mils should not be a concern. Please refer to the layout of the EVM or the other board you are using.

    If the length is expected to be more, you might have to do a simulation to ensure you are following the 

    7.13 Multimedia Card (MMC) Interface requirements in the datasheet.

    Please be sure to provide the recommended terminations - Series and parallel.

    Akshay V said:

    we are planning to use the SD Card in Highspeed mode.

    Whether the AM3356 processor supports this speed..?

    What type of SD Cards(UHS-1..etc.) can be used along with the MMC0 of AM3356..?

    Please read through the below chapter. This is a software related query that you might want to start a thread or add to the above thread.

    Chapter 18 SPRUH73Q–October 2011–Revised December 2019 Multimedia Card (MMC)

    From the hardware capability STANDARD MODE and HIGH-SPEED MODE are supported.

    Regards,

    Sreenivasa