🚀 go-pugleaf

In article <9BDBC58@xds13.ferranti.com> peter@ficc.ferranti.com (Peter da Silva) writes:
>[...]
>
>The use of the defined standard RS-232 lines, such as DTR, for transmitting
>such out-of-band data, or the use of the break signal, is clearly superior.
>The only reason the +++  sequence is still used is because it's the convention
>Hayes established when it had a virtual monopoly in the field. And the only
>reason that it was used in the first place was the poor design of micros'
>serial ports back in the late '70s and early '80s.
>
>[...]

Be fair now.

The +++ mechanism allowed users and application writers to manipulate
the modem without having to worry about how to twiddle hardware control
lines.  If you could talk _thru_ the modem, you could talk _to_ the
modem.

That's a _big_ advantage over not being able to control the modem unless
you could find a way to twiddle the control lines in some strange way.
I remember a modem (I've forgotten who perpetrated it upon me) which
expected to be talked _thru_ with RTS asserted and talked _to_ with
RTS released.  Drop RTS, give it commands to dial the phone, raise RTS
to talk to the other end of the link, drop RTS to give it more commands,
etc.; and I remember the hassle these things caused.  Hayes "+++" was
like a breath of fresh air.

-- 
mitchell@mdi.com (Bill Mitchell)