[Elecraft] [KX3] RS232 xcvr control when serial ports are occupied

[Don Wilhelm]

The computer is the DTE device, and those devices designed to connect to 
the computer via the serial port are normally wired as DCE devices.

The original thought when the IBM PC serial port was designed was that 
the PC would be used as a terminal connected to a modem, thus the 
decision was that the PC should be a DTE - and for the first several 
years the PC was used only as a terminal device.  Yes, I was involved 
during those early days, but not as a part of that decision making 
process - I was involved with the IBM PC modems.  My manager said I had 
"M" engraved on my forehead.

Now we have the situation where the computer is the controller.  It 
would be very confusing to change the wiring of the computer, so it 
remains as a DTE, and connecting devices (while not modems) are 
configured as a DCE,

73,
Don W3FPR

On 7/8/2018 10:15 PM, Cady, Fred wrote:
> Hi Andy,
> 
> Don is correct.
> 
> Here is a little blurb that might help.
> 
> http://www.ke7x.com/home/miscellaneous-k3-information/unexpected-agc-behavior/rs232-interfaces-1
> 
> 
> ________________________________
> From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> on behalf of Don Wilhelm <donwilh at embarqmail.com>
> Sent: Sunday, July 8, 2018 7:21 PM
> To: ANDY DURBIN; elecraft at mailman.qth.net
> Subject: Re: [Elecraft] [KX3] RS232 xcvr control when serial ports are occupied
> 
> Andy,
> 
> No TXD is TXD all the way through the path.  Yes, the DTE TXD will have
> the drivers, and the DCE will have receivers, but it is TXD from end to
> end.  RXD is the other way around because the DCE drives that line.
> Trsnsmit and receive are named with respect to the DTE.
> 
> 73,
> Don W3FPR
> 
> On 7/8/2018 8:39 PM, ANDY DURBIN wrote:
>> "TXD is really pin 3."
>>
>>
>> One end's TXD is the other end's RXD. That's obvious to those who have used RS-233 for a while but if someone needs to ask then it may not be obvious. Find the TXD pin on the source and connect it the RXD pin on the destination. Sometimes it's easier to look with a scope than to try to understand the documentation.
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