Ethernet hardware with the CM4
Hi All,
I am developing a system for a customer and part of it is the CM4, used for ethernet. Page 6 on the CM4 datasheet does clearly outline how to connect the CM4 to an RJ45 MagJack but my customer does not want to use an RJ45 but rather a 10 pin Molex connector. What I did is added the needed magnetics (749020111A from Wurth).
I am attaching the relevant schematics.
If someone with CM4/Ethernet experience can please verify that I routed all the nets correctly it will be a great help!
Thank you!
Nir.
I am developing a system for a customer and part of it is the CM4, used for ethernet. Page 6 on the CM4 datasheet does clearly outline how to connect the CM4 to an RJ45 MagJack but my customer does not want to use an RJ45 but rather a 10 pin Molex connector. What I did is added the needed magnetics (749020111A from Wurth).
I am attaching the relevant schematics.
If someone with CM4/Ethernet experience can please verify that I routed all the nets correctly it will be a great help!
Thank you!
Nir.
- Attachments
-
- CM4 Ethernet.jpg
- CM4 Ethernet.jpg (317.46 KiB) Viewed 449 times
- dp11
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Re: Ethernet hardware with the CM4
What's L1 doing ? it isn't on the CM4IO board.
Re: Ethernet hardware with the CM4
L1 is a ferrite bead meant to filter the 3.3V coming from the CM4 3.3 output pin.
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Re: Ethernet hardware with the CM4
Why do you have it ? CM4IO board doesn't have it.
Re: Ethernet hardware with the CM4
Maybe it is not a must. I think that in any case it does not do any harm.
But my question was aimed more at the nets running from the CM4 to the magnetics and from the magnetics to the connector. Anything missing? badly connected?
Thank you
But my question was aimed more at the nets running from the CM4 to the magnetics and from the magnetics to the connector. Anything missing? badly connected?
Thank you
- dp11
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Re: Ethernet hardware with the CM4
I'm not sure how you can say it does no harm. You are feeding power into the ethernet phy on the CM4 !. Before you go too far I suggest you read up on ethernet and termination in particular and compliance testing. NB C5 termination is incorrect for ethernet.
Re: Ethernet hardware with the CM4
Would you be so kind and let me know what do i need to change in my schematics to make it work well with the CM4?
Thank you
Thank you
- dp11
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Re: Ethernet hardware with the CM4
You need to copy the CM4io board. Remove L1. You need to copy the termination in the mag jack. See the msg jack datasheet. This is standard Ethernet termination.
Re: Ethernet hardware with the CM4
I have updated the schematics. Can you please take a look?
Thank you,
Nir.
Thank you,
Nir.
- Attachments
-
- LAN.jpg
- LAN.jpg (198.87 KiB) Viewed 297 times
- gotaf80307
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Re: Ethernet hardware with the CM4
Capacitors (or termination to be more specific) on PHY->magnetics circuitry are critical to get right (in order to have ethernet working). In this case, search and use reference material related to "Voltage mode" PHY. The first material I suggest is CMx documentation. The main thing is that do not use termination capacitors the same way as you use capacitors for power line filtering.
Also pay attention feeding voltage outside of "CM4_3.3V" to CM4 IO pins. Looks like there are a couple of such scenarios (LAN LED and GPIO4) and maybe more on SWx signals.
Also pay attention feeding voltage outside of "CM4_3.3V" to CM4 IO pins. Looks like there are a couple of such scenarios (LAN LED and GPIO4) and maybe more on SWx signals.
Re: Ethernet hardware with the CM4
Thank you. I have read about voltage mode PHY and have changed the schematics accordingly. Would you mind taking another look and letting me know if this design will work?
Thank you,
Nir
Thank you,
Nir
- Attachments
-
- LAN.jpg
- LAN.jpg (52.73 KiB) Viewed 246 times
- dp11
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Re: Ethernet hardware with the CM4
Four capacitors on the phy side is better than two but I suspect you won't notice the difference. It good you have finally removed L1 I'm not sure why that was so hard. As gotaf80307 says reading the documentation is critical and they are correct :
Again just copy how the CM4IO board wires up the LAN LED.Also pay attention feeding voltage outside of "CM4_3.3V" to CM4 IO pins. Looks like there are a couple of such scenarios (LAN LED and GPIO4) and maybe more on SWx signals.
- gotaf80307
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Re: Ethernet hardware with the CM4
Based on the screenshots, RJ45 connector with mags is highly recommended. Dealing with high speed signals it is more than just connecting signals. If this is a hobby or a learning project, then.... well.. you may try something that is unsupported or not commonly recommended, but I think a word customer was mentioned.
Are 22nF capacitors included in a reference circuit?
Are 22nF capacitors included in a reference circuit?
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Re: Ethernet hardware with the CM4
The 22nF are in the magjack are are important if non compliant POE injectors are used.
Re: Ethernet hardware with the CM4
If the 8 way Molex connector actually connects to an off-PCB RJ45, or a long cable, there is debate on whether 75 Ohms is the correct termination impedance, or whether it should be 50 Ohms.
https://resources.altium.com/p/bob-smit ... t-ethernet
Always interested in innovative audio startups needing help and investment. Look for InPoSe Ltd or Future Horizons on LinkedIn to find me (same avatar photograph)
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Re: Ethernet hardware with the CM4
Yep. I think this is probably going beyond what the OP is interested in.
Re: Ethernet hardware with the CM4
Well mention of 'customer' and not using RJ45s implies it could be in a noisy application, possibly in a vehicle where noise floors really count.
Always interested in innovative audio startups needing help and investment. Look for InPoSe Ltd or Future Horizons on LinkedIn to find me (same avatar photograph)
- gotaf80307
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- Joined: Wed Feb 14, 2024 11:28 am
Re: Ethernet hardware with the CM4
It might be nice if the Magjack symbol used in the CM4IO reference design actually represented what was inside the Magjack.gotaf80307 wrote: ↑Wed Nov 12, 2025 12:41 pmExactly. Since I do not recognize such signals I suspect at least one of the reference circuits honeybee still uses is not related to the target design.
Always interested in innovative audio startups needing help and investment. Look for InPoSe Ltd or Future Horizons on LinkedIn to find me (same avatar photograph)
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