Support Question of the Week: Viewing MISO Message Length with I2C / SPI Host Adapter and Control Center Software

Q: Can you help me with the Aardvark SPI Host Adapter? I'm using the Control Center Software, which I expect to allow the MISO messages to be 4 kB long, but the  picture below shows the maximum length of each MISO message is 64 Bytes.

Customer Results of MISO Messages from Aardvark I2C / SPI Host Adapter] Figure 1: MISO Messages from Aardvark I2C / SPI Host Adapter

My question: How can I verify the entire message is sent in the transaction log?

A:  Thanks for your question! The Control Center Software Manual is being updated; the updated version will be available the end of August, providing more information about MISO messages. In the interim, we can provide the information that answers your question today.

The current version of the Control Center manual section 4.2 pages 27-28 provides the following information about the message lengths:

  • "MOSI (Master Out, Slave In): "The maximum message size is 4 KiB due to operating system buffer limits."

The updated Control Center manual will also provide the following information:

  • "Set MISO: The maximum message size is 64 bytes due to buffer limits."
  • "If more bytes are requested in a transaction than have been specified in the set response, the response string will be wrapped as many times as necessary to complete the transaction."

To view the full message length, we recommend sending SPI data between two Aardvark adapters, and a separate Control Center Software instance for each Aardvark adapter. Instructions are provided below. Note that the MISO message is set before the MOSI message.

For the SPI Slave MISO Message:

  1. In the Control Center—Slave "MISO Message" text field, enter more than 64 bytes. For this example, we used  "AA BB 555555555555...555555555CCDD".
  2. Click "Set MISO" and "Enable".
  3. Verify that the Transaction Log in Control Center—Slave shows the "Length" for  "W/R: S" is 64 bytes, as shown in Figure 2 below.

For the SPI Master MOSI Message:

  1. In Control Center—Master "MOSI Message" text field, enter 317 bytes. For this example, we used "EE1111...1111FF".
  2. Click "Master Write".
  3. Verify the transaction log shows the length of 317 bytes in both Control Centers as shown in Figure 2 and Figure 3 below.
    • The Aardvark master sends 317 bytes to the Aardvark slave including the 317 bytes in the MOSI message in Control Center—Master.
    • The Aardvark slave sends to 317 bytes to the Aardvark master 317 bytes in Control Center—Slave.

The screen shots below show the results.

Viewing Full Length of MISO Message with SPI Host Adapter Figure 2: MISO Message for Slave SPI Host Adapter
Alt: Viewing Full length of MOSI Message with SPI Host Adapter Figure 3: MOSI Message for Master SPI Host Adapter

Note: In the Control Center Software, a message is entered in hexadecimal format. The Control Center software automatically inserts spaces  for easier viewing; these extra spaces are not sent in the transaction.

For more information, please see the following documents:
Aardvark I2C/SPI Host Adapter
Aardvark I2C/SPI Host Adapter Data Sheet
Control Center software

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 support@totalphase.com.

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