Star Point Grounding

Star point grounding in a D-Link managed POE switch.

I was poking around inside a D-Link DES-1228P fast ethernet managed power over ethernet (POE) switch. I’m looking into building a few pieces of equipment that are POE and curious how the “big boys” do it.

Opening the device reveals a large main board with several large Marvell ASICs. The large TQFP in the upper right is a Marvell 88E6218, an ARM 9 with 7 switch ports (quick search does not reveal a datasheet). Immediately above the Marvell SoC is RAM and to the right, flash. Next to the flash is what appears to be a JTAG connector. To round out the 24 ports on this switch, a number of Marvell 88E6095 8 port managed fast ethernet with three gigabit uplinks.

D-Link DES-122P overview. Power supply upper left, main board, smaller POE board lower middle.

On the upper left is an adequate power supply. On the main board, just below the power connector are two switching power supply modules. Above the main board is a smaller PCB containing what appears to be much of the POE controller hardware. The ribbon cable goes to front panel LEDs and indicators. J4 by the ribbon cable may be a serial port.

All in all it’s an interesting bit of gear, priced right with useful web and CLI management tools. Just wish it was GigE..