sbrio 9642 digital input maximum input frequency

[Gil_Maor]

Hello,

I would like to know what is the maximum input frequancy for the sbrio 9642 24V DI.

Thanks for your help

Gil Maor

[ColdenR]

Hello Gil Maor,

The manual for the sbRIO-9642 (http://www.ni.com/pdf/manuals/375052c.pdf) does not list the maximum input frequency for the 24V digital input. However, it does list two other pieces of information. On page 45, it lists:

Setup time -- 1 μs max
Transfer time -- 7 μs max

These terms are defined at the bottom of the page:

Setup time is the amount of time input signals must be stable before you can read from the module

Transfer time is the maximum time FPGA Device I/O functions take to read data from the module

So if you have a perfectly formed square wave coming in, the FPGA would need 8 μs to interpret a digital value. So the signal would need to have a period of >16 μs in order for the FPGA to read both the positive and negative values. Therefore the theoretical maximum input frequency would be 62.5kHz for the 24V DI. 

[Gil_Maor]

Hi Colden, thanks for your reply, does this frequancy also apply if I do not use FPGA?

[ColdenR · Accepted solution]

If you use NI CompactRIO Scan Mode (http://zone.ni.com/devzone/cda/tut/p/id/7338), then your maximum update frequency is 1 kHz. Scan Mode still uses the FPGA, but it does not require you to write any FPGA code. To learn more about the scan interface, read the link above as well as this one:

http://zone.ni.com/devzone/cda/tut/p/id/7693#toc1

Now if you're using a counter with scan mode, it can read in counter inputs at a high rate - it will just update the real-time code at a slower rate (maximum of 1 kHz). 

[Gil_Maor]

Thanks