Thank you, John. I want to be able to send a string of data using the "serout" command and trigger the scope about the time that the "stop" bit is xmitted. This will allow me to get a more precise measurement of the turn around time of the device that I'm xmitting to. I plan to send a "pulsout" to trigger the 555, and trigger the scope when the 555 times out (by adjusting the 555 timeout period I should be able to place the timeout close to where I want it). From what I've been able to see; the turnaroud time is about 3.1Msec on some of the xmitted commands, and about 400usec on others. This will be repetitive using a "do" loop inmy program. Jims