What’s New in the SLZB U-Series Devices — And Why It Matters
Share
The new U-series coordinators represent a true hardware upgrade over the previous, now-superseded models. While firmware improvements continue across the range, the U versions introduce fundamental architectural changes that unlock new capabilities, improve stability, and significantly extend long-term flexibility.
Here’s a clear breakdown of what’s changed — and why these upgrades are important.
1. USB Passthrough Mode (The Reason It’s Called “U”)
The defining feature of the U-series is USB passthrough over Ethernet / Wi-Fi.
You can now connect almost any USB radio stick directly to a U-series device and expose it to Home Assistant over the network. For example:
- Plug in a Z-Wave USB stick
- Keep the built-in Zigbee radio
- Result: multiple radios available remotely over Ethernet
On MRxU devices, this means you can effectively run three radios over the network from a single box.
This is not a simple firmware update — it required a full hardware redesign, which is why older models cannot gain this feature retroactively.
Originally, “U” stood for USB, although some users like to call it “Updated”
This also means you can add additional radios (such as ZWA-2 or ZBT-2 USB sticks) and expose them cleanly via the network.
2. Massively Increased RAM for Future Features
U-series devices include 2.5 MB of RAM, compared to just 520 KB in the previous generation.
That’s nearly 5× more memory, enabling:
- More advanced firmware features
- Better buffering and reliability
- Headroom for future protocol and platform updates
Even if you don’t “need” the extra memory today, it’s a major future-proofing advantage.
3. Hardware Flow Control Support
U devices add proper hardware flow control support for radio SoCs — something that was not available on non-U models.
In practical terms, this improves:
- Serial communication reliability
- Stability under high traffic
- Performance in dense or busy networks
From a pure technical standpoint, this won’t always be visible in small setups — but it becomes increasingly relevant as networks grow.
4. Configurable RJ45 Ethernet LEDs
A small but welcome quality-of-life improvement:
Ethernet port LEDs can now be switched on or off.
Perfect for:
- Bedrooms
- Living rooms
- Professional or discreet installations
- Racks where visual noise matters
5. Improved Ethernet Stability
The U-series is built around an updated Ethernet SoC, delivering:
- Better link stability
- Fewer edge-case dropouts
- Improved long-term reliability
This is especially important for coordinators designed to run 24/7, often in central network locations.
6. Dual-Radio USB Exposure on MRxU Models
On MRxU devices specifically, there’s another interesting upgrade:
When connected to a PC via USB, both internal radios can be exposed simultaneously.
For example:
- One USB device for the CC26 radio
- One USB device for the EFR32 radio
- Single cable, two devices
While USB mode isn’t the primary design goal of SLZB devices (Ethernet is), this feature adds flexibility for testing, development, or niche use cases.
Summary
The U-series isn’t a minor refresh — it’s a structural upgrade:
- USB passthrough over the network
- Significantly more memory
- Improved Ethernet hardware
- Better long-term stability and flexibility
If you’re upgrading from a non-U model or planning a new installation, the U versions are the clear choice for anyone who values expandability, reliability, and future-proof smart home infrastructure.