timeout period for rs485

[GaryZ21]

Does anyone know what the time-out timing resolution is on the PCI 485/4 card?  Is it possible to set the time-out to the microsecond value, or is that a OS dependent issue? 

Has anyone tested the time it takes from the point when the tx line stops transmitting to the point when the rx line can start receiving data, if my com ports are configured in the 2-wire mode. 

[LoganS]

As far as I know, the timeout is an OS dependant issue. I haven't done the test you ask about, however you might consider using a utility like portmon to monitor the lines on the serial port. Once again, I believe that only millisecond timing is going to be available.

Logan S.

[GaryZ21]

Question 1:

If I set my com ports to a 2-wire mode.  What is the operating status of the Tx and Rx line when nothing is being transmitted?  Are they both always active or are they active when a start bit comes onto the line?  I read from somewhere that the Rx is on always but the Tx is only active when it is transmitting.  Is that true? 



Question 2:
How do you read or verify the value sent to the RS485 line?  Is the correct value read when you take the  Tx+ minus the Tx- line, or can you read the correct data when you read Tx+ or Tx- with references to ground using the oscilloscope?