Why Is My USB Serial Device Slower Than Other Serial Interfaces? Hardware: Instrument Connectivity Other>>USB>>USB-232, Instrument Connectivity Other>>USB>>USB-232/2, Instrument Connectivity Other>>USB>>USB-232/4, Instrument Connectivity Other>>USB>>USB-485, Instrument Connectivity Other>>USB>>USB-485/2, Instrument Connectivity Other>>USB>>USB-485/4
Problem: I have a USB serial interface, like the USB-RS232, and when I run code, it is significantly slower than running the same code on any other serial interface (like a built in serial port). Why is this happening? Solution: This is a driver related issue regarding our USB serial products. The original cause of the issue came from a 30ms delay when not transmitting data in multiples of 64 byte chunks. As this happens quite often in serial communication, read and write cycles will see a buildup of delays in the hundreds of milliseconds. Installing NI-Serial 3.4 should fix the delay problem: the 30ms delay will be reduced to only a few milliseconds. NI-Serial 3.4 includes new firmware for USB and ExpressCard serial interfaces. If you are upgrading to NI-Serial 3.4 from a previous version, you should disconnect and reconnect your USB and ExpressCard devices to update to the latest firmware after finishing the NI-Serial 3.4 installation process. In the case of the USB-485/4 hardware, you should also disconnect and reconnect the power cable. After the installation of NI-Serial 3.4, the USB serial interfaces should have comparable speeds with other serial interfaces. Related Links: Drivers and Updates: NI-Serial 3.4 - Windows 2000/Vista x64/Vista x86/XP Attachments:
Report Date: 12/17/2007 Last Updated: 09/12/2008 Document ID: 4GGFI8YW |
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