With a series resistor you get an R-C filter together with the pin capacity. So you can calculate the delays. The value of the pin capacity is a bit a guess and depends on the PCB and package type.
I normally calculate with 6 pF per pin. The I get the following values:
Andy, I first thought your cutoff frequency was off a bit and I was going to challenge this but I decided the best way was to try this out and put a resistor in series with the serial receive and test this out in Tachyon by interactively changing the baud rate. From my tests the comms runs fine at 115.2k baud with 250k while 2M baud runs fine with 20k.
I know for practically all my sensing inputs that 100k would be fine and it also means that it can tolerate much higher voltages such as 24V etc. It would be very rare to actually sense signals in the MHz range so the 100k is in fact a very all-round value and if the resistor was rated for mains voltage it could probably tolerate that too!! (don't try this at home kids). I tend to use 100k series input in my PLC style controllers for this reason.
Comments
With a series resistor you get an R-C filter together with the pin capacity. So you can calculate the delays. The value of the pin capacity is a bit a guess and depends on the PCB and package type.
I normally calculate with 6 pF per pin. The I get the following values:
Andy, I first thought your cutoff frequency was off a bit and I was going to challenge this but I decided the best way was to try this out and put a resistor in series with the serial receive and test this out in Tachyon by interactively changing the baud rate. From my tests the comms runs fine at 115.2k baud with 250k while 2M baud runs fine with 20k.
I know for practically all my sensing inputs that 100k would be fine and it also means that it can tolerate much higher voltages such as 24V etc. It would be very rare to actually sense signals in the MHz range so the 100k is in fact a very all-round value and if the resistor was rated for mains voltage it could probably tolerate that too!! (don't try this at home kids). I tend to use 100k series input in my PLC style controllers for this reason.