DP83TC812R-Q1: 125MHz clock output function

Jass Jin

Part Number: DP83TC812R-Q1

Tool/software:

Hi expert,

My customer need 125 MHz reference clock for RGMII. They said that industrial PHY usually has a pin to output 125MHz clock, because PHY will generate one internally.

Why automotive PHY don't have similar function?

Thanks!

3 months ago

0 David Creger 3 months ago

TI__Mastermind 24531 points

Hello Jass,

RX_CLK is generated by the PHY for RGMII communication. This is pin 27 of DP83TC812.

RX_CLK is 25Mhz in 100Mbps mode. Your customer must be referring to 1000Mbps communication, in which the PHY will generate 125Mhz RX_CLK. If this is needed, you may check out DP83TG721.

Thanks,

David

0 Jass Jin 3 months ago in reply to David Creger

TI__Intellectual 2185 points

Hi David,

It's not the RX_CLK, it's the reference clock for MAC in MCU side. MCU need a 125M clock to generate TX_CLK in RGMII.

0 David Creger 3 months ago in reply to Jass Jin

TI__Mastermind 24531 points

Hi Jass,

Can you please share which MCU is being used? Most MCUs will utilize a crystal oscillator as the reference clock.

Thanks,

David

0 Jass Jin 3 months ago in reply to David Creger

TI__Intellectual 2185 points

Hi David,

The MCU is TC387 from Infineon, it does not have PLL to generate 125M from 25M crystal.

0 David Creger 3 months ago in reply to Jass Jin

TI__Mastermind 24531 points

Hi Jass,

I believe you will need to use an external 125Mhz oscillator. Let me double check this and get back.

Thanks,

David

+1 David Creger 3 months ago in reply to David Creger

TI__Mastermind 24531 points

Hi Jass,

I confirmed that 125Mhz reference clock generation is not possible from PHY. Please use an external 125Mhz oscillator for the MCU.

Thanks,

David

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DP83TC812R-Q1: 125MHz clock output function