Illustration by Geralt
Question from the Customer:We are using the Aardvark I2C/SPI Host Adapter as a Master for checking the SMBus on one of our development platforms. Here is a high-level overview of our setup:
While checking the AC Timing Characteristics of SMBus at 400KHz, we see that the Clock Low time (T-low) is less than what the specification shows: measured time 1.08us vs. specified minimum time 1.3us). Here is a screenshot of our measurement:
The timings of other signals are within specification.
Our questions:
Thank you for your questions! There are many factors to consider when using an I2C device to work with SMBus. We will start with adjustments you can apply to the Aardvark adapter, then go over the advantages of using the Promira Serial Platform to more easily interface with your SMBus system.
High capacitance affects timing. Here is an outline of considerations:
To achieve the fastest throughput, we recommend sending as many bytes as possible in a single transaction (i.e., a single call to the Aardvark API). For additional information, take a look at the Aardvark SPI Signaling Characteristics. However, there are limitations:
For your requirement, we recommend using the Promira Serial Platform. With the GPIO pins and Promira Software API I2C/SPI Active, you can create a signal with 50% (or other ratio) duty cycle, which should render good results.
When the duty cycle is required, the setup is 50%: on_time_in_ms = off_time_in_ms. Similarly, the delay time can be manipulated based on the duty cycle required. As described for the Aardvark adapter, there are delays to consider as described below. However, since the switching speed of 100Hz-400Hz is not very high, these delays might not be prominent.
For more details, please refer to Is there a Way to Adjust the Duty Cycle of the I2C Master Clock? Here is additional information about using the Beagle I2C/SPI Protocol Analyzer for monitoring and decoding SMBus data: SMBus and PMBus Using Total Phase I2C Tools.
We hope this answers your questions. Additional resources that you may find helpful include the following:
If you want more information, feel free to contact us with your questions, or request a demo that applies to your application.