Offering 5 MHz, the I2C Ultra Fast-Mode (UFM) is the fastest I2C mode available. It is specified in chapter 5.4 of the I2C-bus specification and user manual.
This mode differs considerably from other I2C modes:
- UFM works unidirectionally; data is sent in one direction only
- Ultra Fast Mode lines are driven in push-pull technology
- Slaves do not send an acknowledge bit
- There is a single master only
- No arbitration for a multi-master environment is available
- Nevertheless, multiple devices can be addressed sharing an I2C UFM bus. 112 nodes are available.
Full timing tables are in chapter 6.3 of the I²C-bus specification and user manual (UM10204)
The UFM bus basically focuses on LED devices; NXP, for example, offers the LED controller PCU9656.
Why I2C Ultra Fast-mode (UFm) Disappeared From the Market
Introduced by NXP to push the boundaries of the traditional I2C bus, the Ultra Fast-mode (UFm) promised data rates up to 5 Mbit/s. By replacing open-drain lines with push-pull drivers and dropping the bidirectional acknowledgement (ACK) bit, UFm aimed to supercharge LED drivers and displays.
However, this specialized variant is now effectively obsolete. Major semiconductor manufacturers, including NXP, have discontinued active production of UFm masters and peripherals (such as the PCU series). By stripping away I2C’s native bidirectional feedback, UFm lost the core advantages of the standard while failing to match the raw performance of SPI. Today, developers requiring high-bandwidth, low-pin-count communication rely on SPI or the modern MIPI I3C standard, leaving UFm as a brief footnote in hardware history.