In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Tracy Allen wrote:

Hi William, 

[u][url=http://forums.parallax.com/forums/default.aspx?f=7&m=58271#m58954]This message[/url][/u] has results of tests I made on the SX comparator.    I found that the common mode range went much lower than 0.4 volts.  On a 5 volt supply it worked from 0.05 volts up to 4.9 volts, although above 4 volts the accuracy (offset) was degraded.   The propagation delay degrades below 0.1 volt and above 3.8 volts.

While I agree that in general a qualified RS485 driver is a good bet, it is also true that short, local  RS485 connections seldom use the 120 ohm termination.   When that is the case, the SX could drive the line with no problem.    There are other reasons for using the qualified parts.  They can operate into an extended common mode voltage, (like -7 to + 12  volts), as might occur if the ground potentials are different at the two ends.  Some modern drivers can survive large ESD spikes or accidental connection to power lines as might occur in an industrial environment.  Isolated drivers can operate into and survive huge insults to the RS232 line.   But if none of those considerations are going to apply to what you are doing,  and you have short and well controlled RS485 with >1000 ohm termination, then the SX direct. could hack it.

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