I²C bus assignments

The per-(sub-)bus identifiers for(/on/of) Linux-enabled UltraZohm systems are listed like [so].

I²C on ≥Rev05 carriers

• I²C0 (PS_I2C0) [0]: “User bus” (I2C_USR) with eight-channel I²C switch

  • ASlots_I2C [3]: Per-card “UZP EEPROM”s

  • DSlots_I2C [5]: Per-card “UZP EEPROM”s and card-specific functions

  • CPLDs_I2C [4]: Primary I²C controllers of D slot CPLDs (1V8)

  • I2C_SEC [7]: Secondary I²C controller of S³C (1V8)

    • On Rev05 carriers, this bus is Missing pull-up resistors on spare I²C bus (Rev05)

    • On ≥Rev06 carriers, this bus also controls the I²C GPIO of the slot disable feature

  • I2C_FP_isoIOs [2]: IsoIOs on Frontpanel Mainboard (Rev01) and Frontpanel Mainboard (Rev02)

  • BP_T/BP_B [8/6]: Backpanels

  • Spare [9]: On ≥Rev06 carriers, this bus can be accessed via X3 (NB: pull-up Rs needed!)

  • The bus switch/multiplexer (U6) can be reset via a MIO GPIO, which is helpful in case of bus lock-ups, e.g., due to downstream issues on cards etc.

• I²C1 (PS_I2C1) [1]: “System bus” (I2C_SYS)

  • SOM_I2C: SoM PLL and EEPROM

  • I2C_PRI: Primary I²C controller of S³C (3V3)

  • I2C_SYS_3V3: Carrier “UZP EEPROM”, frontpanel (system bus; used, e.g., for the MAC EEPROM required/included on Ethernet-enabled frontpanels), and thermal management

I²C on ≤Rev04 carriers

[for reference only, please see Overview of the ARM Pins et al. and their schematics for details]

• I²C0 (PS_I2C0_*) [0]: SoM & adapter cards

  • SoM I²C (PLL and, perhaps, EEPROM)

  • A adapter card slots (3V3)

  • D adapter card slots (3V3)

  • D adapter card CPLDs (1V8, unused as of 2025)

• I²C1 (PS_I2C1_*) [1]: Outside (connector)

  • Available on X10 (3V3)

  • Used by the I²C/SSD/S²C Extension Board retrofit (≤ Rev04) board