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

Mon Jul 9 12:16:47 EDT 2018

I still use a black box brand breakout box!! Indispensable to a field communications technician!

Ronnie W5SUM

Sent from my iPhone

> On Jul 9, 2018, at 11:04 AM, Dave Fugleberg <dave.w0zf at gmail.com> wrote:
> 
> As a ‘field engineer ‘ for a global company in the 80s, I’d occasionally
> find one of those RS232 breakout boxes tucked behind some production
> system, jumpered to make the connection work, blinking away, because some
> technician finally hit upon the magic combination and then left it in place
> rather than building a proper cable.
> I’ve seen lots of devices whose designers took great liberty with the RS232
> standard...a breakout box and some gender changers was indispensable in
> working with a variety of serial devices. Sometimes even that plus a
> healthy amount of experience wasn’t sufficient, as when marginal voltage
> swings, extra long cables, and different ground potential at each end
> conspired against you.
> Lots of fun!
>> On Mon, Jul 9, 2018 at 10:10 AM Cady, Fred <fcady at montana.edu> wrote:
>> 
>> Thanks Don.  It must have been interesting working all that out.  I used
>> to enjoy giving my students a history lesson explaining the control and
>> handshaking signals in the RS232 connector from basic principles, starting
>> with the Bell 103 modem.  That didn't help  explain the terminology and
>> signal naming problem that Andy had. Manufacturers were terrible at keeping
>> to the standard.  And really, in isolation, it doesn't make sense that a
>> signal named TxD would be a input and not an output.  Documentation was
>> scanty and so the scope, or my favorite test tool -- the RS232 Blinky Box
>> -- had to be gotten out to tell what was what.
>> 
>> The now  used for other purposes signals are:
>> DTR -- from the terminal to the modem to tell the modem the Data Terminal
>> was ready.  Now used for CW or PTT.
>> 
>> DSR -- From the modem to the terminal to indicate the modem was ready
>> (generally power on).
>> 
>> The Bell 103 could send data only in one direction at a time so RTS and
>> CTS were included to control the flow of the data.
>> 
>> RTS -- Request to Send from the terminal to the modem to request the line.
>> 
>> CTS -- Clear to send from the modem to the terminal to say the line was
>> not busy and to go ahead with sending the data.
>> 
>> RTS and CTS were also used to control the data flow from a fast device to
>> a slow device.  I think there were some kenwood radios that used this
>> scheme.
>> 
>> DCD -- Data Carrier Detected was used for the modem to tell the terminal
>> that the carrier from the other data set was being generated (the phone
>> line was working).
>> 
>> RI -- Ring Indicator asserted by the modem when it heard a ringing signal
>> at the other end of the telephone line.
>> 
>> As I remember it.
>> 
>> Cheers,
>> Fred KE7X
>> 
>> 
>> 
>> 
>> ________________________________
>> 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 10:04 PM
>> To: elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] [KX3] RS232 xcvr control when serial ports are
>> occupied
>> 
>> 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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