Hello, While this may be possible, it isn't recommended. The serial port on your computer has a UART with a clock that will clock out whatever byte LabVIEW writes to it one bit at a time along with start bits, stop bits, and parity bits at the baud rate that you specify. LabVIEW can certainly write a character to the UART over and over again, but due to those framing bits (stop, start, parity) you are probably not going to be able to get a very normal square wave out of the port.
To do any sort of serial communication, just use the shipping example LabVIEW <-> Serial.vi that came with LabVIEW. You can experiment with writing different characters to the UART and see how the data comes out the port (pin 3 on a DB9 connector) with a scope. As far as the serial framing information, you can check this site for more information: http://www.lvr.com/serport.htm Also, the UART was not designed to source much current, so be careful and check the specs on the chip that you have in your computer before doing anything with this square wave. Scott B. Applications Engineer National Instruments
