Can't write to serial port

[JonL]

Hi,

I just bought a serial header for my board and tried to test it through basic serial communication.

What happens is that any 'echo 123 > /dev/ttyS1' command will get nothing on the serial terminal connected to it (Putty, on Windows).
On the other hand, reading from it (with cat /dev/ttyS1) works fine.

Using the board's own serial port (/dev/ttyS0) everything works fine.

I checked the /dev/ttyS* permissions and they have rw.

I'm using Squeeze with kernel 2.6.36.

Can you tell me anything to check?

[atreyu]

Have you set the baud rate on it yet?

Check it with:

stty -F /dev/ttyS1

Set it with, e.g.:

stty -F /dev/ttyS1 115200

[JonL]

I didn't configure it, but did a

stty </dev/ttyS1

and got a baud rate of 9600.

[atreyu]

Does your echo command work as expected with the onboard serial port?, e.g.:

echo 123 > /dev/ttyS0

[JonL]

Yes, that works fine.

[atreyu]

If the char device is correct (right maj/min numbers, etc.) and has the write permissions, then you got me.

Anything in dmesg?

Have you put a voltmeter on the pins of the serial cable itself and rung them out, to make sure all the wires are good?

[JonL]

Well, I haven't checked the cable pins, but I have tried with two different ones.

Probably, I'll have to check the header pins with a voltimeter.

[JonL]

Still didn't get around to find myself a voltmeter....

But I noticed that my FTDI USB-Serial converter lits up the RX light when I do the 'echo 123 > /dev/ttyS1', so something is going on in there...

[atreyu]

So what are you trying to do with this serial port? Can you run a null modem cable b/t it and your Windows PC , enable serial login on your Linux box and see if your Windows box can log in (via putty , hyperterm, etc.) in that direction?

[JonL]

I'm testing it, as I want to connect a serial LCD screen to that port.
So, this is still a testing phase on that port.