KSZ9021RNI with 16KB Jumbo Frames and RGMII Timing

ElecSuppliers Part Number GuideSep 06, 2026

The KSZ9021RNI is a triple-speed Ethernet transceiver from Microchip designed for embedded networking equipment using an RGMII connection between the PHY and MAC. It supports 10BASE-T, 100BASE-TX and 1000BASE-T Ethernet and combines configurable interface timing with integrated diagnostics and copper-link management features.

The industrial version is specified for operation from -40°C to +85°C and is housed in a 48-pin QFN package.

Gigabit Ethernet with RGMII Connectivity

KSZ9021RNI supports Ethernet communication at 10Mbps, 100Mbps and 1000Mbps over standard twisted-pair cabling. Its RGMII interface is compliant with RGMII Version 1.3 and provides a reduced-pin connection to Gigabit Ethernet processors and switches.

The PHY supports both half-duplex and full-duplex operation at the supported Ethernet speeds. Auto-negotiation automatically determines the appropriate link speed and duplex configuration for the connected network.

Programmable TX and RX Timing

A useful feature of KSZ9021RNI is the programmable timing available on the RGMII interface. TX and RX signal delays can be adjusted through the PHY configuration registers, allowing designers to compensate for timing differences introduced by PCB routing and MAC interface characteristics.

This approach provides more flexibility during Gigabit Ethernet board development because timing optimization does not have to rely entirely on fixed PCB trace-length adjustments.

The RGMII I/O also supports 2.5V and 3.3V levels, providing compatibility with different Ethernet MAC implementations.

16KB Jumbo Frame Support

KSZ9021RNI supports jumbo Ethernet frames up to 16KB. Larger frame support can be useful in networking equipment that transfers larger blocks of data and needs to reduce packet-processing overhead.

This capability makes the device relevant to embedded networking applications such as network storage, servers, gateways and communication equipment where Ethernet packet size can influence overall data-transfer efficiency.

LinkMD Cable Diagnostics

Beyond basic Ethernet connectivity, KSZ9021RNI integrates LinkMD time-domain reflectometry for copper cable diagnostics. The function can help identify potential cable faults and assist engineers during system development and maintenance.

The device also provides loopback and NAND tree test functions. Automatic MDI/MDI-X operation detects and corrects cable pair swapping, while the PHY can also detect and correct pair skew and polarity conditions.

These integrated functions can reduce the need for additional external diagnostic hardware when testing an Ethernet interface.

Integrated Termination and Power Architecture

The KSZ9021RNI integrates termination resistors for the Ethernet differential pairs, helping simplify the external circuitry around the PHY.

Its power architecture includes an on-chip LDO controller that can support a single 3.3V supply configuration with an external FET used to generate the 1.2V core supply. The transceiver itself operates from a 3.3V supply while the RGMII interface supports the required 2.5V and 3.3V logic levels.

A 125MHz reference clock output is also available for system-level clocking requirements.

Industrial 48-QFN Ethernet Transceiver

KSZ9021RNI uses a 48-pin QFN package measuring 7mm × 7mm. The industrial temperature version is rated from -40°C to +85°C, making it suitable for embedded networking hardware exposed to wider temperature variations.

The compact package can help reduce PCB area while retaining triple-speed copper Ethernet and RGMII functionality.

KSZ9021RNI for Existing Gigabit Ethernet Designs

With programmable RGMII timing, 16KB jumbo frame support, LinkMD diagnostics and 10/100/1000Mbps Ethernet capability, KSZ9021RNI provides a feature-rich PHY architecture for embedded Gigabit networking.

Potential applications include network appliances, gateways, industrial communication equipment, network storage systems, embedded servers and media-conversion equipment. The specific KSZ9021RNI part is now listed as obsolete by major distributors, so it is particularly relevant when maintaining or sourcing components for existing designs rather than selecting a new-generation PHY for a new platform.