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Support Question of the Week: Using the Aardvark I2C/SPI Host Adapter, How Do I Program the Software to Read with a Repeated Start (Sr)?

I am using the AardvarkTM I2C/SPI Host Adapter with a PMBus (Power Management Bus) device. The protocol of the PMBus device requires a Repeated Start (Sr). The Read Byte protocol looks like this:

S-SlaveAddress(7)-Wr(1)-Ack-Command Code(8)-Ack-Sr-SlaveAdress(7)-Rd(1)-Ack-DataByte(8)-Ack-P

I do not want a Stop between the Write and Read portions of the transaction. Can the Control CenterTM Software GUI accommodate this? The only obvious buttons are Write and Read. I see the AardvarkTM Software API has a function called "i2c_write_read". I need to program the software to read with a repeated Start (Sr)  – which application would work best for this?

Thank you for your question! The Control Center Software was recently updated to v3.56. This new version includes features that match your requirements. To update the software, we recommend you install the latest Control Center v3.56 for your computer.


Using Control Center Software v3.56 with the I2C "Master Register Read" Option Figure 1: Control Center Software


The Control Center v3.56 "I2C Master Register Read" option can be used for your system requirements. The typical protocol to read a register on an I2C device performs an I2C write with the register address, which is followed by a repeated start and an I2C read. The "I2C Master Register Read" feature provides a way to do this in one operation. For detailed information, please refer to section 4.1.2 of the Control Center User Manual.

The Aardvark API function "Master Write-Read (aa_i2c_write_read)" writes a stream of bytes to the I2C slave device followed by repeated start and a read from the same slave device. For additional information please refer to section 5.5.3 of the Aardvark Host Adapter User Manual.

For additional information, please refer to the following documents:

Control Center Software User Manual
Aardvark Host Adapter User Manual
Aardvark Software API
Total Phase Products
Product Selector Guide

We hope this answers your question. If you have other questions about our host adapters, software or other Total Phase products, feel free to email us at sales@totalphase.com or submit a request for technical support.


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