I'm developing a board set for the sbRIO-9607. When power is applied to the RIO, it appears that all the FPGA pins are driven high for ~50-100ms. Is this the expected behavior?
I'm using pull-down resistors. And after the bitfile is loaded (~45 seconds after power-up), all the pins that are designated as outputs work correctly. Thanks.
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On page 40 of the following document, you can see that all DIOs are floating before and during FPGA configuration. You need to use a pull-up or pull-down resistors to ensure start-up values. What value are you using on pull-down resistors?
NI sbRIO-9607 Single-Board RIO OEM Devices: http://www.ni.com/pdf/manuals/375463a.pdf
Besides that, what concerns me the most is that you mentioned that the bit file lasts ~45 seconds to load. Are you loading the bit file from the flash memory? 45 seconds sounds a lot to load a bit file.
Thanks for the reply.
I understand that the FPGA-IO will be tri-stated upon between power-up and the loading of a bitfile. We are using 10k pulldown resistors on all outputs.
Sorry if I wasn't clear about the timing. It takes 45 seconds for the OS and RT-EXE to load, which then flashes the bitfile as one of the first operations (the bitfile itself takes less than a second). I was just trying to make the point that after normal loading, everything seems to function fine.
Our issue is with the first 50-100ms after power is applied the sbRIO board. All outputs seem to assert themselves high during this time, and then go into tri-state.
What kind of accessories are you using to access the board outputs? I will try to reproduce this behavior. Are you using an oscilloscope to verify this?
I'm using a NI-9694 RMC breakout board --> ribbon cables --> custom PCBs. The PCBs have various functions -- 24V digital inputs and outputs, 24V PWM outputs, high frequency inputs, etc. All pins are buffered and opto-isolated. I can send you some of the PCB schematics if you think that would be useful. Thanks.
Have you tried using lower resistance pull-down resistors? I would suggest trying 220Ω or something around. Maybe 10k is a lot of resistance and it is not being able to pull the output down.
I can try a lower valued resistor, but I'm not sure how that would make a difference. The pin should be tri-stated on power-up, so any reasonable resistance should pull the pin down to ground.
Any other ideas/explanations? Thanks.
Due to the available power on the output when it is tri-stated, a 10 kiloohm resistor might not be pulling it down to ground. In order to provide you with a more efficient and dedicated support please give us a call at 866-275-6964 (866-ask-myNI) and one of our engineers will create a Service Request to continue assisting you.
After some more digging/troubleshooting, it looks like the issue lies with the powerup sequence of one of the breakout boards. Sorry if I wasted any of your time, and thanks for the help.