// application note

AN0018 Moving a bus from SMBus at 3.3 V to I3C at 1.8 V with the Binho Supernova

A device that starts on an SMBus bus at 3.3 V and moves to I3C at 1.8 V needs the host to find it, check that nothing SMBus-only is left on the bus, lower the bus voltage and assign it a dynamic address. The Supernova does all of this from one I3C port. This note supplies a script that runs the five steps, with SETDASA or ENTDAA for the last one, and shows it on a bench where a second Supernova plays the I3C device: 20 of 20 runs with SETDASA and 20 of 20 with ENTDAA, with the bus high level measured at 3.34 V before the change and 1.79 V after it.

Products: Binho Supernova
Protocols: I2C I3C
Topics: SMBus to I3C
Revision: Rev 1.0 · November 6, 2026

// outcomes

What you'll walk away with

This document covers:

the five steps of the sequence and the pyCosmicSDK call behind each one
the wiring, and where the bus pull-ups must go so that they follow the voltage change
a script that runs the sequence, with SETDASA or ENTDAA as the address assignment
measured results on a bench with a Supernova as the I3C device

It does not cover the SMBus to I3C Basic detection flow of the PCI-SIG out-of-band management specification (Hot-Join, ARP, the SMBus reset), which AN0014 covers, or MCTP and NVMe-MI messages.

// background

Background

Some devices power up as SMBus targets at 3.3 V and can move to I3C at 1.8 V. The host decides when: it first makes sure that every device left on the bus can follow, then lowers the bus voltage and assigns dynamic addresses. A device that only speaks SMBus would not survive the move, so the host stays in SMBus mode if it finds one.

The Supernova's I3C port speaks SMBus (legacy I2C) and I3C on the same two pins, and its voltage is set from software. The whole sequence therefore runs from one port and one script.

// applicable devices

Applicable devices

Role	Part	Identifier	Basis
Controller	Binho Supernova	hardware revision C, firmware 4.6.2, I3C HV port	measured, this document
Controller	Binho Supernova	firmware 4.6.0 or later	expected: every call used is in 4.6.0
I3C device	Binho Supernova as I3C target	hardware revision C, firmware 4.6.2	measured, this document
I3C device	any device that answers on SMBus at a static address and supports SETDASA or ENTDAA		not measured

// what's covered

What's covered in the note

01 Introduction
02 System overview
03 Hardware setup
04 Software setup
05 Procedure
06 Measured results
07 Troubleshooting

The full procedure, measured results, and reference code are in the PDF and the assets archive.

// materials

What you'll need

Binho Supernova USB host adapter for I3C, I2C, SPI & UART View product

Software Mission Control 3 or the Cosmic SDK (Python, C / C++ / C#). Get the software

Files The reference scripts and assets used in this note. Download the assets

// our edge

We don't just follow the I3C spec.

We don't watch from the sidelines. Plugfest after plugfest, our team is in the room where vendor I3C implementations come together — finding edge cases, debugging quirks, and validating real silicon against the spec.