We are using BCM5482SA2KFBG PHY for ethernet link in SGMII mode by selecting INTSEL = 2'b10. The PHY was supposed to establish a link upon power up using Autonegotitation without any management configuration. PHY auto-negotiates to 10Mbps half duplex, though the PC and the PHY are capable of 1Gbps. The same 2 PHYs establish 1Gbps link with each other. Is there any other setting that is supposed to be done?? enter image description here This is how we have connected the interfaces as shown in the schematic.

Test cases: enter image description here

In this test, 2 different Broadcom PHYs in different boards(identical boards but not in the same board). The PHYs link up at 1Gbps (Autonegotiation - Autonegotiation done bit is high). We even created data traffic from one board and the data was received correctly in the other board.

enter image description here Test 2: This is what we aren't able to understand. The PHY does not connect to PC most of the times. We have to disable the SGMII interface for the PHY to link-up with PC (at 10Mbps with Autonegotiation). How does the SGMII interface affect the working of PHY ??

Test 3: We have another board with Marvell PHY which links correctly (1Gbps - Autonegotiation). Same PC, same ethernet.

  • \$\begingroup\$ perhaps BCM5482SA2KFBG ? (not 45... do you have datasheet? artwork, test method? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 16 '19 at 6:06
  • \$\begingroup\$ How confident are you in the return loss of your layout , CMRR from the balun and 1nF to earth ground to 0Vdc \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 16 '19 at 6:22
  • \$\begingroup\$ @SunnyskyguyEE75 I have updated the schematic on how we have connected. I am really not skilled to answer the other questions(Still very confident with the layout/schematic). \$\endgroup\$ – Sudarshan shenoy Jan 16 '19 at 7:25
  • \$\begingroup\$ If the stripline/microstrip is not right, it wont work \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 16 '19 at 7:55
  • \$\begingroup\$ Not at full speed \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 16 '19 at 9:58

The problem was with input frequency to the PHY. We were giving wrong frequency to the PHYs, but since the frequency was same on both the boards, they had no problem connecting at full speed with each other.

  • 1
    \$\begingroup\$ I've accidentally built 50 Mbps Ethernet once as well. It was fairly obvious what was wrong when running a speed test. \$\endgroup\$ – Simon Richter Feb 28 '19 at 8:05

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