ETH PHY: KSZ8091RNA versus LAN8742

[peter-h]

Can anyone offer a view on these two?

I am using the LAN8742 which is slightly cheaper. The KSZ8091RNA has some curious functions like a back to back mode for making an ETH repeater without a CPU... It also has some curious diagnostics but in an embedded system application you can't usually report anything anyway. It is also not clear if the STM32 supports it; there is a standard part to the management interface, plus a vendor-specific part.

Both are Microchip but I suspect MC bought up two companies to get these two chips. The pinout is totally different.

I would change from the LAN8742 only to get lower power.

[bingo600]

Can anyone offer a view on these two?

I am using the LAN8742 which is slightly cheaper. The KSZ8091RNA has some curious functions like a back to back mode for making an ETH repeater without a CPU... It also has some curious diagnostics but in an embedded system application you can't usually report anything anyway. It is also not clear if the STM32 supports it; there is a standard part to the management interface, plus a vendor-specific part.

Both are Microchip but I suspect MC bought up two companies to get these two chips. The pinout is totally different.

I would change from the LAN8742 only to get lower power.

My gut feeling is that the K.... Phy's came from Micrel

/Bingo

[PDP-1]

I have used both, started off with the LAN8742 and had to go to the KSZ8091RN(A/D) when I couldn't find any of the old kind in stock. I just got my KSZ8091 running earlier today.

Other than the different footprints the changeover was pretty transparent to the code. I'm only using 'standard' register stuff and both chips were strapped to come up in auto-negotiation, I don't think I changed anything in my driver software to talk to them.

If you did want to try the vendor-specific stuff it should be trivial, you already have the ability to read/write to the PHY registers so the rest is just playing with bit flags.

I did find the documentation for the LAN8742 to be somewhat clearer and easier to read.

[peter-h]

The KSZ makes some claims re power management which made me wonder whether it would save significant power where ETH is used with a low duty cycle (which is usually going to be the case with 100mbit ETH). I found the PHY portion draws quite a lot of power. I posted about it here
https://www.eevblog.com/forum/microcontrollers/how-fast-does-st-32f417-enter-standby-mode/msg4064983/#msg4064983

[Scrts]

I've used KSZ9021, KSZ9031 and some 10/100Mbps part I can't remember the PN. All worked very well.