Most Significant Bit Not Sent using Serial Communication?Hardware: Serial
Problem: Why is the most significant bit sometimes left out in serial communication? For example, when I want to send FFFFFF the value that is actually sent is FF7F7F. Solution: The problem arises on Windows 2000 and XP and is caused by the Windows Serial Device Driver version 5.1.2. Installing Windows Service Pack 1 or LabVIEW 6.0, 6.1, or 7.1 will fix the flaw in the driver. LabVIEW 7.0 does not install a fix for the problem. The problem is also resolved in LabVIEW 8.0 or later. You can verify this is the problem by setting up Hyperterminal to send all FF's in hexadecimal. Use a program such as Portmon to monitor the serial port. You will find that you get 7F after the first initial complete FF. Portmon is a utility that allows you to monitor and display all serial and parallel port activity on your system. If you have 2 serial ports, you can also use the attached LabVIEW programs to verify the problem is resolved. Use the Send.vi to send FF and the Receive.vi will stay as FF if the problem is resolved. If the problem still exists, 7F will be seen on Receive.vi Related Links: KnowledgeBase 1M9D8H6Q: Serial Communication Starting Point External: Portmon for Windows Attachments:  send.vireceive.vi
Report Date: 12/13/2004 Last Updated: 01/16/2009 Document ID: 3GC9JAQG |
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