Support Question of the Week: How does the Aardvark I2C/SPI Host Adapter indicate ACK and NACK in I2C mode?

I am using the AardvarkTM I2C/SPI Host Adapter.  I am trying to understand the symbols in a captured trace:

(2013-11-21 11:35:12) [S] <50:w> 00 [P]
(2013-11-21 11:35:12) [S] <50:r> aa aa 55 55 [P]
(2013-11-21 11:35:12) [S] <50:w> 0a 00* [P]
(2013-11-21 11:35:12) [S] <50:w> 04 [P]
(2013-11-21 11:35:12) [S] <50:r> 00 00 00 00 00 00 [P]

I have three questions:

  • [s] - I assume this is the start bit – is that correct?
  • What is [P] ?
  • How can I see if the ACK is high or low?

Thank you for your questions! When the Aardvark I2C/SPI Host Adapter is running in I2C monitor mode, S is start bit, P is stop bit, and there is no indication for ACK bit.

 

Using the Aardvark I2C/SPI Host Adapter in I2C Mode Figure 1: Aardvark I2C/SPI Host Adapter

 

Because there is no ACK on data bits, the character “*” during the acknowledge (ninth) clock pulse indicates acknowledged or not acknowledged as follows:

  • Acknowledge: When the Aardvark adapter is in I2C monitor mode and the SDA remains low during the ninth/acknowledge clock pulse on data transfer. In this case, the signal is defined as Acknowledge (ACK) and there is no “*” in the end of the data bits.
  • Not acknowledge: The Aardvark adapter is in I2C monitor mode and the SDA remains high during the ninth/acknowledge clock pulse data transfer. In this case, the signal is defined as Not Acknowledge (NACK) and there is an “*” in the end of the data bits.

For additional information, please refer to section 3.1.6 of the I2C Bus Specification and User Manual.

For monitoring the I2C with greater detail, we recommend using the Beagle I2C/SPI Protocol Analyzer. The Beagle I2C/SPI analyzer is a non-intrusive bus monitor, and a more robust and faster device.

 

Beagle I2C/SPI Protocol Analyzer for SPI Signal Monitoring Figure 2: Beagle I2C/SPI Protocol Analyzer

 

The Beagle I2C/SPI analyzer monitors I2C up to 5 MHz The Aardvark adapter I2C monitoring is a legacy feature and up to 125 KHz. Moreover, the Aardvark adapter is a more general purpose device that can actively communicate on the bus, and provides master and slave capability along with SPI/I2C features. For more information, please refer to the following documents:

Aardvark I2C/SPI Host Adapter
Aardvark Adapter User Manual
Beagle I2C/SPI Protocol Analyzer
Beagle Protocol Analyzer User Manual
Total Phase Products
Product Selector Guide

We hope this answers your question. If you have other questions about our Host Adapters 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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