Why is the Most Significant Bit Left Out for Every Other Byte in a 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. 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. Related Links: KnowledgeBase 1M9D8H6Q: Serial Communication Starting Point Portmon for Windows Attachments:
Report Date: 12/13/2004 Last Updated: 02/06/2008 Document ID: 3GC9JAQG |
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