[GreenKeys] DTE etc

[Peter Gottlieb]

"Circuit terminating" and "Communications" are equivalent in this context.

While it is true not all manufacturers follow the spec, most do, and you 
are correct in regards to when you need a straight through vs. null 
modem cable.  Think of it this way:  The original basic system consisted 
of a serial comm device (TTY or equivalent), a modem, some 
interconnecting channel, another modem, and another serial 
communications device.  If you want to connect two TTYs together, you 
need a cable to act like the modems, hence, a "null modem."  This is 
necessary due to the TTYs always sending on one pin and hence they would 
conflict, and both receiving pins connected together would receive 
nothing.  In the comm network there is a reversal where data received on 
one port is transmitted on another.  The null modem cable thus acts like 
the entire comm network.

The devil is in the details, which I spend years tearing my hair out 
over in the design of X.25 packet systems and asynchronous Front End 
Processors.  Fortunately, never again.

Peter



eugene at hertzmail.com wrote:
> I am likely wrong, but I recall DTE/DCE as Data Terminal Equipment (the
> thing a person uses) and Data Communications Equipment (like a modem).
>
> A DTE connected to a DCE requires a straight through cable (pin 1 to pin
> 1, etc)
>
> Two DTEs connected together require a NULL Modem cable which puts Tx of
> one device onto the Rx of the other and vice versa.
>
> Eugene
>
>
> -----Original Message-----
> From: greenkeys-bounces at mailman.qth.net
> [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of WB6BLV Central
> California
> Sent: Wednesday, May 21, 2008 5:41 PM
> To: GreenKeys at mailman.qth.net
> Subject: [GreenKeys] DTE etc
>
> RS-232 (Recommended Standard 232) is a standard for serial binary data
> signals connecting between a DTE (Data terminal equipment) and a DCE
> (Data
> Circuit-terminating Equipment).
>
> (According to the book RS-232 Connection, the 'standard' is not
> necessarily
> followed by many manufacturers, so some DTE and DCE devices may or may
> not
> function as one would expect from reading the 'standard'.)
>
> John
> WB6BLV at inreach.com
>
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