I was able to test that the presentation software is interfacing with the stimtracker. The problem that I am having now seems to be with the code sequence. I’m not sure I understand the sequencing for communicating with stimtracker.
I see how mp\x0A\x00\x00\x00 = 10, but I’m not sure I understand how mp\xE8\x03\x00\x00 = 1000 from the Presentation wiki (http://www.neurobs.com/wiki/Presentation/Hardware/Other_Devices/Cedrus_StimTracker). Also, it seems that every odd code I send, sends the same code sequence to the Biosemi software (decimal value = 128). Thanks for the help.
Hi Sylvia G
Not sure if you are using http://www.cedrus.com/support/stimtracker/tn1465_activetwo.htm?
If you are sending event code make sure that you are checking on the bits that correspond to what ever you want to record.
The link above shows
Event marker bit 0 Trig. 8 / 128
Event marker bit 1 Trig. 9 / 1 (MSB)
Event marker bit 2 Trig. 10 / 2
sending event marker on every bit will signal a corresponding decimal values in your BioSemi Software (I assume?)
See my posting if it will help you 
http://community.cedrus.com/showthread.php?t=1844
Cheers
Al
The mp command sets the pulse duration for subsequent uses of the mh command. But the mp command will not send a pulse if used by itself.
Meanwhile, a new web page was created this morning that illustrates how to use a terminal emulation program to send commands to StimTracker. It could serve as a useful stepping stone prior to writing code that interacts with StimTracker.
Thank you so much for the response. It was very helpful. I was able to download and install the RealTerm software and was able to get the “Markers” Blue LED light on the front panel of the StimTracker to activate. I think the problem must be with how I setup the BioSemi Actiview software because I’m still not seeing the corresponding 255 value on the EEG computer.