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ADA2200 SPI Configuration and Control Questions

Question asked by doctek on Dec 8, 2015
Latest reply on Dec 22, 2015 by brianharrington

I have designed a lock-in amplifier using the ADA2200. It seems to be working as expected, but now I am trying to tune its behavior using the SPI port and am running into some issues. In all of the following, I am writing to one register at a time. I have verified that I can read and write to the SPI registers by observing the behavior of the part. I have also looked at the questions posted to this forum and not found the answers I seek. Here are my questions.

1. The data sheet implies that it is possible to reset the ADA2200 using the SPI port. If 0x80 is written to port 0x0000, the entire chip should be reset. Reset is cleared by writing 00 to the same port. The core only (whatever that exactly means) may be reset by writing 0x01 to 0x002d, and released by writing 0x00 to the same port. I have tried both of these sequences. As soon as I write the ADA2200, the RCLK stops and will not resume until I press the /RST button. Sending the same initialization sequence I use to configure the chip initially does not work until I assert and release /RST. That is not at all what I expect! I have tried both advertised modes of reset, and have tried a delay of 1 second between asserting and lifting the reset commands. Why doesn't this work?


2. What I want to do is to toggle between I and Q signals. I am trying to do this by setting/clearing the appropriate bit in register 0x002a. Is that sufficient?


3. The larger question is: When do changes to the control registers take effect? Is it immediately as soon as the change is sent, or are there dependencies, like on the states of other registers?

 

4. What is the timing of the writes to the control registers? At least one response to a question about the SPI port implied that a delay of 500 milliseconds between writes is required. Is that delay required? I want to experiment with the timing of SYNCO next, so I need to know this.

 

Thanks for your help with this. The ADA2200 is a great part!

 

PS. I would attach my schematic and my code, but I only see an "Attach Image" button. What types of files are allowed?

 

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