Hi all,
I just wonder if someone else did make the same measurements.
We do have a system with a 9572XL having inputs with an external
47KOhm resistor. The design has done by another person. I prefer pull-up resistors in the 3.3K...10K max value ranges.We did have strange behavior until I did measure the voltage on these inputs pins. After configuration through JTAG we do have a clean 3.3VDC pulled up input value ...
Bringing one of these inputs to GND and releasing it again, shows with the oscilloscope, that the voltage on these pins doese rise until
0.9Volt but not higher. Thought the external pull-up resistor should bring these inputs - only - in the design back to 3.3VDC again. No way, once these pins have been brought to GND, the release of it give us a voltage rise up to 0.9VDC but not more.This explains a lot, why even the simplest logic did give us a real blues ...
However reducing to the external pull-up resistors to below 10K, we found everything is working as expected. Checking the datasheet a see a max input current for the inputs of +-10 uA. Multiplying this value with 47K gives us 0.47V max ...
It seems that this max value is somehow not the max value .... (On these inputs, there is no additional cap ...)
Any idea?
Markus