Serial Port (RS-232) problem

[RU482]

I have an engineering sample tablet PC that runs Windows XP. This tablet has a serial port to connect to devices like legacy serial printers.

The problem I am seeing is that as soon as the tablet gets into windows, it sets the TXD and RTS pins to a high logic level (+6V, approximately).

If I boot into DOS from a bootdisk, the logic stays at low levels (-6V)

Is there something in windows that configures the serial port at boot up?
I'm thinking this might be an oversight by our manufacturer.

Thanks!!!

 

[Lord Evermore]

I think the number of people at the forums these days who've ever even USED a serial port is probably in the fractions of a percent range.

I don't know the answer with any certainty. Presumably it's related to the drivers, I assume that a high signal is sent to the port continuously so that when you plug something in, it immediately knows that the UART is ready to communicate. Normally one would expect a specific software package accessing the serial port to be the one to set this when you actually are ready to use the port, but maybe it has something to do with being able to immediately detect devices that are plugged in, for PnP purposes and automatic hardware installation.

I don't have any serial ports enabled to even look at Device Manager. There may be some configuration or initialization information there, and you might be able to put in a config line to make Windows do something other than its default.

Maybe this would help you? http://www.eltima.com/products/serial-port-monitor-control/

 

[rcalzada51]

You may want to visit the Microsoft Windows XP Tablet page. Visit the Expert Zone. You can get tips, free downloads, and talk to experts who can answer your questions about running a tablet PC with Windows XP.