RS232 no output to oscilloscope.

[boki]

Dear All,
I am trying to scan RS232 output (TX) signal by an
oscilloscope.

When I short my RS232 output pin.2(TX) & pin.3(RX), it function work (
sometimes lost some words, at least it sent signals).

When I connect RS-232 TX to oscilloscope, connect oscilloscope ground
to pin.1(Earth ground) or pin.7(GND logical ground), oscilloscope both
never has signals. If I 'short' RS-232 pin.2(TX) and pin.3(RX), it
works!

Why?


Thank you very much for your answer.

Best regards,
Boki.

 

[boki]

pbdelete@spamnuke.ludd.luthdelete.se.invalid wrote in message news:<4163e336$0$175$cc7c7865@news.luth.se>...

boki <bokiteam@ms21.hinet.net> wrote:
Dear All,
I am trying to scan RS232 output (TX) signal by an
oscilloscope.

When I short my RS232 output pin.2(TX) & pin.3(RX), it function work (
sometimes lost some words, at least it sent signals).

When I connect RS-232 TX to oscilloscope, connect oscilloscope ground
to pin.1(Earth ground) or pin.7(GND logical ground), oscilloscope both
never has signals. If I 'short' RS-232 pin.2(TX) and pin.3(RX), it
works!

Check that it works with another computer to make sure you haven't burned your
rs232 output.

Oscilloscope shield to pin.7
--""-- signal to pin.2 (try 3 aswell!)

Set 5 Volts/Div
Set sweep speed to approx 1 bit per Div. 9600 bps should be 100 us/Div.

1. It still work not burned-out yet.
2. Yes, I connect them as same as below:

Oscilloscope shield to pin.7
--""-- signal to pin.2 (try 3 aswell!)

3. I had set 3V 3.1V ... 5.8V 5.9V 6V, it still no response.

4. I only add a voltage by hand, and look the output difference(no
change).

I guess, I am wrong at Step4, or the Appication (VB MSCOMM control)
only be trigger at a 'complete' byte not a bit...

Best regards,
Boki.

 

[boki]

cbarn24050@aol.com (CBarn24050) wrote in message news:<20041006084934.25170.00001985@mb-m04.aol.com>...

When I connect RS-232 TX to oscilloscope, connect oscilloscope ground
to pin.1(Earth ground) or pin.7(GND logical ground), oscilloscope both
never has signals. If I 'short' RS-232 pin.2(TX) and pin.3(RX), it
works!

Try connecting your scope to the RX signal, If it sees anything then you have
your Tx Rx transposed, a common mistake, caused by using the wrong gender
connector.

Thank you very much for your reminding, but I think I am lucky to skip
this mistake already s

 

[R. Steve Walz]

pbdelete@spamnuke.ludd.luthdelete.se.invalid wrote:

boki <bokiteam@ms21.hinet.net> wrote:
Dear All,
I am trying to scan RS232 output (TX) signal by an
oscilloscope.

When I short my RS232 output pin.2(TX) & pin.3(RX), it function work (
sometimes lost some words, at least it sent signals).

When I connect RS-232 TX to oscilloscope, connect oscilloscope ground
to pin.1(Earth ground) or pin.7(GND logical ground), oscilloscope both
never has signals. If I 'short' RS-232 pin.2(TX) and pin.3(RX), it
works!

Check that it works with another computer to make sure you haven't burned your
rs232 output.
--------------------

Can't burn it out by shorting it!

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public

Oscilloscope shield to pin.7
--""-- signal to pin.2 (try 3 aswell!)

Set 5 Volts/Div
Set sweep speed to approx 1 bit per Div. 9600 bps should be 100 us/Div.