Looking for dialup hardware solution

James Knott james.knott-bJEeYj9oJeDQT0dZR+AlfA at public.gmane.org
Sun Jul 13 12:07:42 UTC 2008

Evan Leibovitch wrote:
> phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org wrote:
>>> There are some USB-to-DB9 serial adaptors but I don't know how well they
>>> handle the complexities of RS-232 modem control.
>> For what it's worth, we found that USB-Serial control includes hardware
>> flow control (RTS-CTS handshaking).
> Good to know. It's just that I have too many recollections of the
> nightmares I had with breakout boxes trying to make various kinds of
> modems work with various kinds of serial ports. If only hardware
> handshaking was always just RTS/CTS. :-)
> (On a DB9 cable things weren't that bad, there weren't too many ways to
> screw up that spec. On a DB25 pinout -- like the kind on Walter's
> Sportster modem -- there are many more ways to complicate things (In
> fact I recall that DTR/DSR hardware handshaking was at least as or more
> important than RTS/CTS, in the heyday of these modems.)
> Does the USB-DB9 adaptor support all eight pins (we can do without Ring
> Indicator, but let's not forget the venerable Carrier Detect ;-) )?

For standard modems, the exact same signals were used whether on 9 or 25 
pin connectors.  It was only when you got to synchronous modems, where 
you had to worry about clocks etc., that things got more interesting.  
However, there were a lot of devices that weren't quite following the 
spec and required changing connections to get them to work.

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