No Voltage on ExRes1 w/ W5500

Question

Hi everyone! I’ve created a PCB with the W5500, the schematic is according to the reference schematic. Now I can access and write all of the registers on the W5500, the Duplex and Speed LEDs work if I set the mode manually and the Crystal seems to be oscillating at 25.0007MHz (though my oscilloscope is not great, so I don’t now if that measurement is accurate). I can see the link pulses from my switch arriving on the TX and RX pins of the W5500, probably due to the AutoMDX feature. However, I don’t get a link. I’ve poked around the board a bit and I have 1.2V on the TOCAP and 1V2 pins and 3.3V on the respective input pins, but 0V on the Exres pin. What could be the cause for this? My lines to the RJ45 jack are a bit longer than usual (approx. 2 - 3 cm), but I don’t think that this should bring down the link entirely. I rather feel that something might not be correctly set up or supplied. Any ideas what might be the reason? Any input is appreciated!

Eugeny · Answer

Philipp_K: However, I don’t get a link. What does it mean? Link LED does not turn on? Switch does not see port connected?

Eugeny · Answer

Philipp_K: PHYCFG register does not have any unexpected contents. What does it have exactly when cable is connected and when it is disconnected?

Philipp K · Answer

If I use autonegotiation, it has 0xF8, which makes sense to me: Reset inactive, Autonegotiation all capable, duplex and speed not (yet) set, no Link. Is there any procedure I have to follow? Right now I am doing the following: HW Reset, wizchip_init(), setting netinfo, configuring PHY, 300ms pause, PHY reset, 300ms pause BTW, the Wiz5500io board works with the same cable and switch setup (without anything connected to the SPI, i. e. only automatic configuration by the companion processor)

Philipp K · Answer

I’ll upload my schematics in a minute, maybe you can have a quick look at it; I’ve double and triple checked most of the things (including solder connections), though and the signal from the switch gets through well, there’s just no signal coming from the W5500 pins. The missing voltage on the resistor and at the respective pin on the chip hints at something being wrong with the PHY. Nevertheless I appreciate all suggestions and will gladly try out all of them!

Philipp K · Answer

DMXInterface.pdf (230,7 KB) This is my schematic, the RJ45 connector footprint has been provided by the manufacturer. The missing 1M resistor on the oscillator has been added as a THT part. Let me know if you see something unusual. Thanks!

Philipp K · Answer

Hi, thanks for checking my design! The Layout should be okay as well, since pulses get through and furthermore the connections seem to be the way they should be when measuring them. Maybe I didn’t esplain my problem well: It should be sufficient if one endpoint, e. g. the switch supports auto-MDX. The switch, not the W5500, is trying to auto-negotiate using auto-MDX, so it sends Links pulses down both wire pairs. I can only see those pulses on the board when the switch is present. At the same time, the W5500 apparently ´doesn’t see or understand those pulses (which look good to me) nor does it send anything back on either line, so the switch does not turn its link LED on, which leads me to believe that the PHY just does not work as intended, but I don’t know why that might be. The Wiz5500io seems to have 1.2V on the ExRes pin, while my design has 0V, other than that, the levels seem okay. Any idea what might cause this difference? Attached you will find the Link Pulses I see on the lines. osc.zip (5,2 KB) Eugeny: Must work with your switch though, but you may try changing cables and try another switch to see if there will be a difference. I’ve already tried with different cables and endpoints (switch, router, laptop, etc…), but to no avail. As I said, it seems to generally work with the W5500 when I use the Wiz5500io breakout board from WizNet. I’ve also used both 33R and 0R as damping resistors, currently I am using the latter, since this seems to have worked for some people and EMV should only be a minor issue while on my desk.

Eugeny · Answer

Ok, thank you for summary. You configure PHY using PHYCFGR, and you said it is F8. What are the states of PMODE wires? What resistors are soldered in? Reading the datasheet: When W5500 is reset by POR or RSTn PIN, PHY operation mode is configured with PMODE[2:0] PINs by default. After POR or RSTn reset, user can re-configure PHY operation mode with OPMDC[2:0]. If user wants to re-configure with PMDC[2:0], it should reset PHY by setting the RST bit to ‘0’ after the user configures this bit as ‘1’ and OPMDC[2:0] . I read it as that you must perform two writes, first one setting the PHYCFGR[5:3], and second with PHYCFGR[7] reset (and 5:3 set the same way as in previous write) to reset PHY.

Philipp K · Answer

A while ago, I had the mode wires in Autonegotiation mode, but soldered them to 10M half duplex since I thought this would work. Didn’t help. But the W5500 does accept the reconfiguration, which is performed according to the datasheet: After configuring and then resetting the PHY with the API functions, the Duplex and Speed LED light up accordingly and the register reflects the new values. The configuration does not seem to make any difference for the outcome though. The PHYCFG register indicates that the PHY is turned on, but there never is any reaction on the lines…

Philipp K · Answer

Eugeny: I am out of ideas, only guessing remains. Same here, all I seem to know that something seems to have brought down the PHY. I’m not sure whether it’s broken, though I don’t know why that would be, but I’ve already replaced it once and I am not keen on putting in a third chip since they are not really cheap and I suppose it might harm the board, too. Eugeny: Maybe you can post picture of the board? I will, as soon as I am home. Or would a rendering also be sufficient? Eugeny: By the way, pin 8 of the magjack should be grounded. True! I’ve used a resistor leg to solder it to the case pins a few weeks ago, but that did not make a difference. Once I figure out what the problem is here, I’ll probably make a new version where I adress the minor issues like this, too

Eugeny · Answer

Philipp_K: Or would a rendering also be sufficient? I would say not much. There’re layout guidelines, but bad layout must not cause no link. It may work badly, but not fail completely. Exactly as you said in your original post. Philipp_K: I’ve already replaced it once Then it is not a chip, but something else. This is good news… Check L1. Is it in place? What is the voltage at 3V3A?

Philipp K · Answer

Eugeny: Check L1. Is it in place? What is the voltage at 3V3A? L1 is indeed in place and the voltage is 3.3V. I have used this part. Is it suitable? But I think that on a stable supply it should not make a huge difference. EDIT: I think the impedance at 100MHz might be a bit to high

Philipp K · Answer

I’ve tried bridging the ferrite bead as you suggested, but it didn not make a difference. Would it be possible that while using my oscilloscope probe I slipped and shorted something that wasn’t supposed to be shorted? Usually, most chips can handle that, afaik… And other than Exres1, all levels (3.3V, 1.2V, ToCap, VBG) are okay…

Philipp K · Answer

Hi, I’ve done that already! Resistance from EXRES1 pin to GND is 12.4kOhms +/- 100 Ohms (I’ve usedthe respective resistor, this one specifically), which is below 1%. Anyways, I think the voltage that I see there should be way higher than 0V, rather around 1.2V as you’ve mentioned. Is there any way to verify whether the PHY section of the W5500 is broken?

Philipp K · Answer

Eugeny: Maybe you can post picture of the board? Also, here are some pictures as requested. I am sorry for the low quality but hope that you shall find them useful nonetheless: Photos.zip (400,3 KB)

Philipp K · Answer

Hello everyone, it’s me again. I’ve decided to improve my design (better, shorter differential routing, clock instead of crystal, better filter inductor) and have my boards preassembled to make sure there are no soldering errors. I’ve got a mint condition W5500 breakout board here, with a brand new connector (same parameters though) and with a software that has worked with the official breakout board, too. Well, same problems as before: —No Link —No voltage on Exres —Surprisingly low current consumption —Writing and reading registers works just fine, everything there is as expected. —Reconfiguring the PHY works, but the Link does not work regardless of configuration It feels as if the PHY is in power down mode, even though the corresponding register bits say that it is in auto negotiation mode… For instance, the W5500 consumes ~13mA like in Power down mode instead of 56mA as would be normal in Un-Link mode. Any thoughts on that? I will also send my design soon

Philipp K · Answer

As promised Schematic: Ethernet.pdf (120,7 KB) 3D View of the board Ethernet.PDF (419,6 KB)

Philipp K · Answer

A quick follow-up for anyone wondering or any future person who stumbles across this thread: After posting to another forum, someone pointed out that Pin 11 was wrongly connected to GND instead of 3V3. I must’ve overlooked it due to that pin being grouped with the ground pins. I don’t know who thought that it would be a good idea to create a schematic symbol like that (I took it form the Altium vault). Anyway, thanks to everyone who contributed!