Re: RS-232, No short No send?

From: Boki (bokiteam_at_ms21.hinet.net)
Date: 10/06/04 

Date: Wed, 6 Oct 2004 23:54:43 +0800

Deaer Roger,
                     Yes, I connected pin.3(TXD) to oscilloscope signal and
pin.1 connected to oscilloscope ground.(didn't swap lines)
but there is no signal in oscilloscope. If I short pin.2 pin3, it works.

I am confusing why it didn't send out signals when pin.2 pin.3 are not
short. ( I floting all other pins.,.except signal and ground.)

Best regards,
Boki.

"Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk> ¼¶¼g©ó¶l¥ó·s»D:efS8d.124$J42.116@newsfe2-win.ntli.net...
>
> "boki" <bokiteam@ms21.hinet.net> wrote in message
> news:4c3c095a.0410060345.7b4ea413@posting.google.com...
>> 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.
> Because you are using the wrong pin?...
> RS232 equipment, can either be 'data terminal' equipment (things like
> PC's), or 'data communication' equipment (Modems etc.). These have the
> receive data, and transmit data pins swapped over, as well as the
> handshake lines. Hence a piece of DC equipment, could connect directly to
> a piece of DT equipment, without needing a 'null modem' (which swaps the
> pins over). Connecting two DTE units together, required either a real
> modem, or a null modem to give the crossover. I'd suspect the kit you are
> trying has the data lines swapped, relative to what you expect, and that
> TXD, is on pin 3.
>
> Best Wishes
>
>

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