I’ve been looking for a MCU/MPU with built-in Ethernet connectivity, and I’ve noticed that most only contain a built-in Ethernet MAC interface and require an external PHY.

Why is this the case, as in why do most of these chips not contain both a MAC and a PHY to minimize the number of additional ICs needed?

  • 1
    \$\begingroup\$ should it be cable or WiFi? \$\endgroup\$
    – Juraj
    Dec 16, 2022 at 9:01
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    \$\begingroup\$ @Juraj wifi requires a completely different MAC \$\endgroup\$
    – user253751
    Dec 16, 2022 at 11:51
  • \$\begingroup\$ Combo MAC-PHY chips do exist (like KSZ8851SNL), but I have not seen one chip that includes CPU + MAC + PHY in one chip. \$\endgroup\$
    – user4574
    Dec 16, 2022 at 23:42
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    \$\begingroup\$ Some SoCs such as Allwinner H3 and H6 do integrate CPU (multiple cores, VPU, GPU, etc.) + MAC + PHY, though from what I understand the PHY is connected to the 100-Mbit/s EMAC which has performance issues, while there is a better Gigabit-capable GMAC without PHY. \$\endgroup\$
    – jcaron
    Dec 17, 2022 at 13:44

2 Answers 2


PHY requires some fairly beefy pin drivers as well as analog signal processing on the receive side. The fabrication processes to support this well are not optimized for high-density digital logic, which is what the MAC and the rest of the system require. The PHY also dissipates a significant amount of power all by itself. And sometimes different media require different PHYs, but the MAC can be the same. For all of these reasons, it makes sense to keep it as a separate chip.

That said, there are some chips targeted for embedded applications that include both. Wiznet, for one, has products in this space.

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    \$\begingroup\$ Not exactly. A switch will still have a MAC for each port, but they'll all be integrated into the same chip. \$\endgroup\$
    – Dave Tweed
    Dec 16, 2022 at 4:15
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    \$\begingroup\$ @cdubs Every port requires its own MAC. \$\endgroup\$
    – user253751
    Dec 16, 2022 at 10:13
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    \$\begingroup\$ @cdubs: Yes, absolutely it does. A switch IC will have a MAC for each port, and the port connected to the onboard processor can be connected directly, MAC to MAC, with no PHY needed. \$\endgroup\$
    – Ben Voigt
    Dec 16, 2022 at 15:43
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    \$\begingroup\$ PHY and MAC or even PHY, MAC and switch engine are quite commonly integrated on one chip but PHY, MAC and main system processor rarely are. The embedded world seems to preffer to put the MAC with the processor while the PC world seems to preffer to put the MAC with the PHY. \$\endgroup\$ Dec 16, 2022 at 15:55
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    \$\begingroup\$ I think the lack of all three together may also have to do with the fact that you generally want the PHY to be located close to the Ethernet port itself, while for various reasons the CPU often needs to be located somewhere entirely different, so putting them in the same package would require undesirable compromises in lots of possible use cases.. \$\endgroup\$
    – Foogod
    Dec 16, 2022 at 17:29

A company called Luminary made MCUs with both Ethernet MAC and PHY in one package, however they accomplished that by co-packaging two individual chips.

TI has since acquired them, not sure if they discontinued those particular parts in their entirety. They did discontinue some that we were using, sadly, with no pin-compatible replacements.

The IC processes required for the analog PHY functions and high density lower power digital are generally not well compatible. You'll see a somewhat similar separation of higher voltage/current I/O and of EEPROM memory, for similar reasons.

Multi-chip packages (outside of the memory arena) have become more popular with the relatively recent introduction of chiplets, so we could see more of this kind of thing, though wired Ethernet may not be as compelling as it was some years ago.

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    \$\begingroup\$ The Stellaris line is still available, TM4Cxxx and the MSP432. \$\endgroup\$
    – Lior Bilia
    Dec 16, 2022 at 13:04
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    \$\begingroup\$ @LiorBilia There do appear to be a few members listed with on-board PHY. Limited to no stock, but c'est la vie these days- they are shown as 'active'. \$\endgroup\$ Dec 16, 2022 at 13:39

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