c6747 : questions about hw design

Devin Park

Hi,

We're now drawing h/w schematics for c6747(375Mhz).

1. RMII clock

We'll use an RMII phy. But I wonder if c6747 can supply a 50Mhz clock to the ethernet phy.

c6747 datasheet has the following description and says the RMII_MHZ_50_CLK as "Input or Output". Then can C6747 give a 50Mhz clock to the ethernet phy when its mode is output? We're considering a 25Mhz osc for OSCIN(and dsp is 375Mhz).

AHCLKR0/RMII_MHZ_50_CLK/GP2[14]/BOOT[11]

A4(ZKB)

EMAC 50-MHz clock input or output

2. As I wrote earlier, we'll use an 25Mhz external OSC.

From the website on c674x checklists, I saw the 12Mhz OSCIN.

I wonder if a 25Mhz OSC can be used without issue..

Thanks,

Devin

over 11 years ago

0 Antony Samsunil over 11 years ago

TI__Expert 4760 points

Hi Devin ,

Normally we suggest customer to use external clock oscillator for Ethernet PHY due to jitter tolerance.

Note: Per the RMII industry specification, the RMII reference clock (RMII_MHZ_50_CLK) must have jitter

tolerance of 50 ppm or less.

You can use 25MHz for OSCIN, but make sure it is of the correct amplitude -- 1.2V.

Regards

Antony

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0 Devin Park over 11 years ago in reply to Antony Samsunil

TI__Expert 5965 points

Hi Antony,

I also found the information from TRM & datasheet. So we will use an external OSC for an RMII PHY.

Thanks,

Devin

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c6747 : questions about hw design