NI-845x

[justpeachy]

I’d like to use an NI-845x to capture 6 channels of 14 bit data from an LTC2351 ADC. I get errors using the NI-8451 in conjunction with the SPI streaming API and CVI. A trawl on the internet infers that the SPI streaming API doesn’t work with NI-8451. The same internet sites suggest the NI-8452 “might” work. It has to generate the CLOCK (< 25MHz), the CONVERT strobe and read the resultant 6 x 14 bits out of the ADC on the SPI lines. It seems very straightforward but is the NI-8452 up to the challenge that the NI-8451 failed.

The LTC2351 data sheet is easy to access on the internet; the timing is attached

[AH-NI]

Hi,

For completeness for the rest of the community. I looked into this issue and also had a response from an AE who specialised in this area.

"Based on the datasheet of the ADC, specifically the timing diagram on page 10, this lines up with our SPI Streaming API. The Conv line is called the same and pretty confident the Internal S/H Status is the same as DRDY. The only problem is that the number of bits can only be configured between 4-64 bits. Therefore, I believe you can only successfully communicate with the LTC2351 if you have it configured for 4 channels or less.

As for the scripting API, you still need to specify the # of bits per sample, which is still limited to 64. The scripting tools can run fast once the script is loaded on hardware (this happens when the run script is called) but you would have to loop that run script command which could not happen fast enough to keep up with the streaming ADC. Ultimately, it is possible to use the NI 8452 with that ADC, as long as the ADC is set to send 4 or less channels to that we can remain below the 64 bit limit."
- Chris