Copyright © 2010 Future Technology Devices International Limited

20

Document Reference No.: FT_000204

DB9-USB-RS232 Datasheet

Version 1.2

Clearance No.: FTDI# 130

8 Troubleshooting

Ensure the latest device driver is in use. See www.ftdichip.com

If USB devices other than FTDI chips are installed in the system, then check with all manufacturers of

these devices for the latest device drivers.

Section 3 details driver installation. If the user continues to have driver installation isues, then please

refer to the FTDI installation guides http://ftdichip.com/Documents/InstallGuides.htm for additional

details.

Common Windows Device Driver Troubles:

DEVICE TIMES OUT: The default settings of the device driver assume typical data transfers of

hundreds to thousands or more bytes at a given time. Some applications, such as a GPS device,

only send data in short packets, often only a few bytes. If this is the case, it may be necessary

to adjust the driver buffer size and/or latency timer to smaller values. These values can be

adjusted through the Advanced driver options. The buffer size can be reduced to 64 bytes. The

latency timer can be set as low as 2ms. A setting of 1ms will cause unnecessary USB traffic and

could adversely affect data transmission. Advanced driver options are described in

http://www.ftdichip.com/Documents/AppNotes/AN_107_AdvancedDriverOptions_AN_000073.pdf

ERRATIC MOUSE POINTER: The device driver defaults to query an attached device to find out

whether it is a mouse or modem, consistent with native COM port operation. Some RS232

peripherals constantly send short packets of data, causing the host system to “think” a mouse or

modem has been attached. These short packets will interfere with normal mouse operation

causing the pointer to jump around the screen. If this happens, disconnect the RS232 device and

uncheck the Serial Enumerator option, also found on the Advanced driver options.

COM PORT IN USE: Windows keeps track of all COM port assignments. If multiple FTDIChip

products have been connected to a single system, the COM port number will increase, even if the

other devices are not attached. If the higher COM port assignments are not acceptable for the

application, known unused COM port numbers should be uninstalled according to the FTDI

installation guide: http://ftdichip.com/Documents/InstallGuides.htm.