LAN8742A with Picoblade Connector Instead of RJ45/PHY Layout Issue?

[jabramo]

I have a PCBA design that uses a Molex Picoblade connector instead of RJ45 due to enclosure height restrictions. The PHY IC is a LAN8742A and the MCU is STM32H743VIT6, the ethernet is also POE.

I have spliced, a ethernet and 8pin Picoblade connector together to make a 6in cable that plugs into a router. I figured with such a short distance and being 10/100 that while not ideal should still work. I maintained the RJ45 pinout. There is also a POE circuit using a small Silvertel AG9905 module, that is working as expected.

So far I have not had luck getting a link with the router running a simple webserver page using the lwIP stack. The PHY chip communicates with the MCU seemingly fine. Both PHY and MCU have their own crystals.

The green light on the router is solid and the orange does flash depending on the code, but never gets assigned an IP address.

Im starting to suspect its a design or layout problem. Is there anything in my design that jumps out as incorrect, I followed the LAN8742 application guideline and configuring the LAN8742A IC the same as implemented on the Nucleo 144 board STM753.

Is this most likely to be a shielding issue, differential trace issue, PHY IC layout problem or perhaps code?

[gamalot]

R15, R16, R17, and R18 should be placed right next to the LAN8742A.

[jabramo]

R15, R16, R17, and R18 should be placed right next to the LAN8742A.

When I look at the LAN8742A EVB I think I within a few mm of what they are doing there, do you thing that is the likely issue here? Would 1-2mm closer be the difference of it working or not? Anyway I can verify this, I am not familiar with ethernet communication signals?

[gamalot]

Based on your description, I actually suspect it is more likely a software setting problem. I only mentioned that the termination resistors should be placed as close as possible to the LAN8742A chip because you brought up the layout, and that's what the datasheet recommends. I don't have much experience with this myself, but I would probably try running Wireshark on a PC to capture packets and analyze where the fault might be.

[IconicPCB]

Jabramo

... same same... of say 30 pieces of a prototype run, a half a dozen fail to connect.
I tried a number of different  browsers to not much utility.. The units which did not initially connect  reduced from seven to five. MISERY!!!!!

I then tried to connect to my linux machine via firefox. One hundred percent success.
 I guess You can imagine what the initial OS i tried was... yep.W10.

So go try connecting to a linux machine...it may give you reason to like networking.

[jabramo]

Thanks for all the info everyone. I have made progress but still have some issues that continue to give me trouble.

Some additional details. Of the 10 boards 3 seem to work but not without some issues. They refuse to work off cold boots (from off to powered) they only seem to work after a warm boot of flashing a different binary then flashing with the simple server code.

For the remaining 7 I am able to assign them a static IP and random MAC, and I can confirm this by seeing the device connected on the router UI, but when I ping I get host unreachable. Same code same setup with the 3 others with a warm boot I get the ping back and I can open the simple server test program.

The boards all pass the PHY internal loopback test, but not always first go off cold boot.

I soldered in a magjack RJ45 to bypass the magnetics and picoblade connector. The RJ45 works with the 3 working boards but do not fix the issues with the 7 others. That makes me confident that my issue is not with that side of the circuit and is more so related to the PHY<-->STM32H7 RMII side of the circuit.

I have tried tuning the series resistors up and down from 33ohm. My REF_CLK seems stable. I have bypassed the 3.3V LDO with a lab supply to make sure its not a problem with the power supply. I have added more bulk capacitors to the LAN8742A and the MCU, 10uF everywhere I could find. I have tuned the load capacitors on both the LAN8742A and STM32H7.

I am really scratching my head at what could be going wrong here. Theres always a chance that I have more work to do on the firmware but I cant explain why 3 work and 7 dont with identical setups.

[fchk]

I've completed a workung design with LAN8720A (8742A seems to be the same) and STM32F7.

Main difference: I used a 50 MHz oscillator (ECS-2520MV-500-FN-TR) as a reference clock for the PHY CLKIN and the STM32 ETH TX CLK (PA1) (33R in series to each endpoint). Other than that I don't see major differences.

[gamalot]

I've completed a workung design with LAN8720A (8742A seems to be the same) and STM32F7.

Main difference: I used a 50 MHz oscillator (ECS-2520MV-500-FN-TR) as a reference clock for the PHY CLKIN and the STM32 ETH TX CLK (PA1) (33R in series to each endpoint). Other than that I don't see major differences.

Seems the issue's clock/reset related. Could be worth throwing in a little delay after the STM32 comes up, then reset/init the LAN8742A.

[jabramo]

I have played with the delays extensively.

From my debugger RTT you can follow how I initialize the system

00> --- Hard Reset. RTT Initialized. Fast Blink Delay... ---
00> --- HW RESET: Forcing Straps LOW (RMII Mode)... ---
00> --- HW RESET: Driving PB0 LOW... ---
00> --- HW RESET: Releasing PB0 HIGH (Latching Straps)... ---
00> --- HW RESET: Done. Waiting for PLL... ---
00> --- MPU Configured. Write Buffer Disabled. ---
00> --- Calling HAL_Init... ---
00> --- HAL_Init Done. ---
00> --- Calling SystemClock_Config... ---
00> SCC: Entered. Calling HAL_PWREx_ConfigSupply...
00> SCC: Supply Configured. Configuring Voltage Scaling (Scale 1)...
00> SCC: VOS1 Ready. Configuring Oscillators (HSI First)...
00> SCC: HSI/PLL Init Success. Configuring Clocks...
00> SCC: Clock Config Success. Now attempting HSE override...
00> SCC: HSE Started (Auxiliary)...
00> --- SystemClock_Config Returned. ---
00> --- Peripheral Init Done. Waiting for Voltage Rail to Settle (10ms)... ---
00> --- Voltage Settled. Enabling SRAM Clocks FIRST... ---
00> --- SRAM Clocks Enabled. Checking Cache Status... ---
00> --- DCache was OFF (Cold Boot). Skipping disable. ---
00> --- PHY Soft Reset Complete. ---
00> [IP: 1.123] [MAC: 02..] [Req: 0] [Link: UP]
00> [IP: 1.123] [MAC: 02..] [Req: 0] [Link: UP]
00> [IP: 1.123] [MAC: 02..] [Req: 0] [Link: UP]

Says link up, they even detect a cable inserted but going link down the moment the ethernet is unplugged but is unpingable, server doesn't load on the 7 boards, does work on the 3 boards, but like I mentioned sometimes those need a warm boot to work..

I had the NRST sharing the same net as the STM32H7 NRST line and controlled by button or programmer, I cut the NRST LAN8742A trace and jumpered it to a STM32H7 IO pin so I could hold it in reset until the STM initialized, no difference.

I have probed the REF_CLK of 3 boards, a working, non working and nucleo 144 Z753 for comparison. Looks like I am within tolerance no? I have attached those scope captures of each of the 3 boards REF_CLK, with a 150mhz probe and spring clip.

It seems like the TX lines are working on the non functioning boards but there is a problem with the RX? The router is able to see the device connected at its assigned IP, the MAC is read correctly, but pings from the PC dont receive back.

Also posted my RMII layout if anyone see a problem there.

[gspeed]

You have a complex system, consisting of the PHY/MAC hardware, STM32 HAL drivers, lwip stack and its STM32 HAL port, possibly FreeRTOS, and your application code involving DHCP and even HTTP. Nobody could help you if you just say the connection doesn't work - where exactly does it not work?

The best way to debug a complex system is to break it down into simple subsystems. In this case first the PHY: connect it to a linux computer, watch the kernel logs and see if it reliably completes autonegotiation at 100M full duplex. Then the MAC and its driver: send ethernet raw packets and use tcpdump to see if they're properly received; then try to receive raw packets from the computer; then flood packets in both directions.

[chriselec]

hi,
i have a problem like you, i design a board with stm32, LAN8742A and AG9905. I have 10 boards some of them work fine but some of them only work TX line.