AM3354: MMC traces requirements

Michi Yama

Part Number: AM3354

Hi,

I have one question regarding SD card I/F of AM335x.

My customer would like to extend the trace pattern of the SD card I/F. Because SD card slot is mounted in front of system. And AM3354 is far from sd card slot. This means the trace length between AM3354 and SD card is long.

Is there any trace rule for SD card I/F?

According to the data manual of AM335x, "7.13.1 MMC Electrical Data and Timing" shows the timing requirements. is this only requirement for SD card I/F?

Please let me know.

I appreciate your quick reply.

Best regards,

Michi

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Hi,

Michi Yama said:
According to the data manual of AM335x, "7.13.1 MMC Electrical Data and Timing" shows the timing requirements. is this only requirement for SD card I/F?

Yes, however you should also follow http://processors.wiki.ti.com/index.php/AM335x_Schematic_Checklist#MMC

This document may also be useful:

0 Michi Yama over 9 years ago in reply to Biser Gatchev-XID

Guru 10030 points

Dear Biser-san,

Thank you for your continuous cooperation.

Please see the attached file.

am335x_gpevm_zczbaseboard_rev1_6A_PCBDesignSpecification.xlsx

Please see "Signal Trace Details" Tab in this file. In No.67 Description, it is written the following.

Keep lengths within 300mil of AM335X_MMC_CLK/AM335X_MMC0_CLK/MMC0_CLK/COM_SDIO_CLK

Is 300mil typo? it is too short , I think.

Please let me know.

Best regards,

Michi

0 Biser Gatchev-XID over 9 years ago in reply to Michi Yama

TI__Guru**** 393215 points

This means the lengths must be matched within 300mils.

0 Michi Yama over 9 years ago in reply to Biser Gatchev-XID

Guru 10030 points

Dear Biser-san,

Thank you for your quick reply.

I think 300mils( 7.62mm) is too short for connecting between AM335x and SD card.

And then, please see the "Net Length Check" tab of "am35x_gpevm_zczbaseboard_rev1_6A_PCBDesignSpecification.xlsx".
In #383 AM335X_MMC_CLK, actual length is "2552.381MIL". This value is bigger than "300mil. So I suspects probably this correct value is 3000mil, not 300mil. How do you think this?

Anyway I know user must meet the timing requirement for MMC I/F in AM335x data manual.

I appreciate your quick reply.

Best regards,
Michi

0 Biser Gatchev-XID over 9 years ago in reply to Michi Yama

TI__Guru**** 393215 points

I already explained that this means that the MMC signal lengths must be matched within 300mils. It does not mean that the lengths must be less than 300mils.

0 Michi Yama over 9 years ago in reply to Biser Gatchev-XID

Guru 10030 points

Dear Biser-san,

Thank you for your cooperation.

Please confirm the meaning that you said "MMC signal lengths must be matched within 300mils."

Do you mean the differences of the length of AM335X_MMC_CMD, the length of AM335X_MMC_D[3:0], and the length of AM335X_MMC_CLK must be within 300mils?

For example,

OK ------ AM335X__MMC_CMD : 2000mils, AM335x_MMC_D[3:0] : 1900mils, AM335X_MMC_CLK : 2200mils

NG -------AM335X__MMC_CMD : 1800mils, AM335x_MMC_D[3:0] : 1900mils, AM335X_MMC_CLK : 2200mils -----> Because MMC_CLK - MMC_CMD = 400mils

Is my understanding right?

Please advise me again.

Best regards,

Michi

0 Biser Gatchev-XID over 9 years ago in reply to Michi Yama

TI__Guru**** 393215 points

Yes, exactly. You understand it correctly now.

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AM3354: MMC traces requirements