- Tue Nov 29, 2011 4:01 pm #136342
fll-freak wrote: This would tend to make me think that the SP3485 has built in failsafeThe key word is "unconnected". When connected to something, especially if you have bus termination resistors, it will not fail safe. I suspect that they use weak pull up/down resistors. As I mentioned before some of the Maxim devices do a better job:
resistors and I should not need to add my own. Am I missing something?
The MAX3430 uses a -50mV to -200mV differentialYou might like to read an old article on RS-485 from The Circuit Cellar:
input threshold to ensure true fail-safe receiver inputs.
This threshold guarantees the receiver outputs a logic
high for shorted, open, or idle data lines. The -50mV to
-200mV threshold complies with the ±200mV threshold
Often a system integrator or even a software engineer is given the task of assembling the RS-485 network. The reasoning is usually something like, "RS-485 is just a twisted pair of wires. How hard can that be to hook up?" The answer is, "Harder than you may think."