> Or if you plan on driving an RS232 to RS485 pod, the RTS line is helpful.
>
> Almost all our devices are wired up to look just like a PC on the basis
> that they are generally terminal devices (DTE) not a comms device (DCE)
and
> we may want to plug into a modem.  We use a standard 5x2 way pin header
> (when not using a PCB mount DB connector) and so can use cheap IDC to DB
> cables made in the billions.

Yeah, RTS is how you control the RS485 transmitter enable.  We do the same
thing with the DTE and IDC to DB cables.

So maybe those extra handshaking lines are pretty useful after all?

RS-232 used to be such FUN!  I am joking.  In the mid-80's, I worked for a
local computer store as a tech, and believe me, there were NO RS-232 pinout
standards back then.  I worked on Zenith, IBM, Osbourne, Kaypro, Tandy,
Apple II, NCR, Commodore, TI, you name it.  It was always a big issue trying
to get some customer's serial printer to work with their computer.  Trying
to figure out how to interface these things was really time consuming.  All
I had was a Smart Cable and a bunch of 9-25 pin adapters.  Flick switches on
the Smart Cable until the thing started working.  Of course, the Smart Cable
was not documented as to HOW it did it's thing, so there was no replacing
the Smart Cable with a custom built cable.  That was their racket, just buy
a $100 Smart Cable for every gizmo...

IMO, the least necessary signal is a toss-up between DTR/DSR or RI.  DSR is
usually used to determine if the other unit is powered up.  RI, well, you
know what Ring Indicator does.  You can determine these 2 criteria with
in-band signalling (using a modem, if you get a response character, you know
the other unit is powered up, and if you get the string "RING", you know the
phone line is ringing).  But if you need to interface some simpler
(non-microcontroller) circuitry, you might need DSR and RI.  Example:  if
you have a device that senses a ring or power up on the other unit, and then
powers itself up or comes out of a sleep mode.

On some apps I have the handshaking lines for out-band signalling, such as
delimiting packet boundaries (assert DTR, send data stream, deassert DTR).
Of course this requires special s/w on both ends of the link, you can't do
this with just any old terminal program.

On one app I used the RI input to generate a 120 Hz AC line sync interrupt.
The RI input was connected to an optoisolator circuit, which was connected
to the AC power line.

BTW, the apps I just mentioned will not work with USB-to-RS232 converters.
So you better have a REAL RS-232 port if you want to do anything other than
plain data transfer.

Best regards,
Ivan Baggett
Bagotronix Inc.
website:  www.bagotronix.com


----- Original Message -----
From: "Ian Wilson" <[EMAIL PROTECTED]>
To: "Protel EDA Forum" <[EMAIL PROTECTED]>
Sent: Monday, July 14, 2003 2:43 AM
Subject: Re: [PEDA] OT: DB9 RS-232 serial port on peripherals.


> On 05:43 AM 12/07/2003, Bagotronix Tech Support said:
> > > Pins 2, 3, and 5 only - If I wanted all those handshake lines, I might
as
> > > well use a parallel interface.
> >
> >If there is any chance you may be using a wireline modem or RF modem, you
> >should consider putting DCD (Data Carrier Detect) in also.  That way you
> >know when you have a valid carrier.  So RX, TX, GND, and DCD would be a
good
> >versatile subset of the full signal set.
>
> Or if you plan on driving an RS232 to RS485 pod, the RTS line is helpful.
>
> Almost all our devices are wired up to look just like a PC on the basis
> that they are generally terminal devices (DTE) not a comms device (DCE)
and
> we may want to plug into a modem.  We use a standard 5x2 way pin header
> (when not using a PCB mount DB connector) and so can use cheap IDC to DB
> cables made in the billions.
>
> Ian
>
>
>



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