The lowest resolution you can get with serial theoretically is 4 microseconds due to a maximum transfer rate of 256Kbps. Then again you will still have to rely on the capabilities of the software that is controlling the communications, mainly the Windows serial driver. With the CVI RS232 library you can only specify as small as a millisecond resolution, if this is not low enough you can try using the Windows SDK functions for setting comm breaks but they have no time limiting parameter on them and are generally just called in a loop or depend on a timer construct. Either of these options, which are basically the only ones you have, are not capable of exacting a discrete number of microseconds for a comm break signal.
The best you can hope for really is in the millise
cond range no matter what you do.
Jason Foster
Application Engineer
National Instruments
www.ni.com/ask
