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DP83640: detecting link status

Part Number: DP83640


Hi,

I am working on a project where DP83640 PHY is interfaced with STM32F4 microcontroller on one side and Fiber Optics Trans receiver on other side. The design is,

STM32F4 <=> DP83640 <=> FO Trans receiver.

I would like to detect the Link Status through polling. I am expecting the status register should reflect the current LINK status. In my case, the registers shows the LINK is UP always.

Cable connected: Read registers

PHY_STS = 0x0605

BMSR      =  0x78cd

Disconnect the cable: Read registers 

PHY_STS = 0x0605

BMSR      =  0x78cd

The link is always valid independent of cable status. How to detect link up/down status through reading registers.

Thanks