HP Serial Port Problem

I have HP EliteBook 8570p Notebook
The serial port on the laptop has a problem , when i connect any device to configure it on that serial port , the messages that have been output from the device appears normally , but when i tried to write anything via my keyboard it does not response to any key of keyboard ,  so the com port can read but cannot write.

Trouble Shooting:
1. i installed windows again , the same problem.
2. i used another software differ from hyper terminal , such like Tera term , putty , and the same.
3. i tried many routers , switches from different vendors to see if the problem from the device not the serial port of laptop , but the same
4. i've updated the bios and all the drivers to latest version , and the same.
Who is Participating?
Norm DickinsonConnect With a Mentor GuruCommented:
Have you tested the port with a loopback plug and diagnostic software to see if in fact the hardware is functioning correctly?


Norm DickinsonGuruCommented:
Serial ports are pretty much the opposite of plug and play. You need to set the communications protocols for the particular device you are plugging into the port for speed, parity, stop bit, etc. and there are a lot of combinations. Both devices need to have the exact same settings for the communication to take place correctly. Here is a link to a basic guideline for setting serial communications:
EngAhmedFarisAuthor Commented:
I already verify that the COM port has the same settings on the device need to be configured , but i think if there is mis-configuration it will not read from the device , but in my case the COM port read normally from the device but do not write any thing.
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Norm DickinsonGuruCommented:
Perhaps you need a different cable? Some RS-232 cables do not carry all of the signals from end to end, but rather loop back on the same end to provide false feedback to the port.  See
EngAhmedFarisAuthor Commented:
I changed 3 console cables , and the same problem
Norm DickinsonGuruCommented:
Again, not all cables are designed for full communications across the cable from one end to the other, so it may not be a "bad" cable but one that is designed for only partial communication. It may be worthwhile to pin out the cable with an ohm-meter to determine whether the necessary pins on one end connect to the pins on the other end. Most inexpensive serial cables shortcut this by assuming there will be a signal, so some pins are not cabled thru, but instead the signal on one end is shorted to a different pin on the same end. It is a little confusing but this may help to explain it a little better.
EngAhmedFarisAuthor Commented:
I have usb to serial connector , and i used these cables with that connector and it works perfectly.
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