Question about modems

[Warner Losh]

On Thu, Nov 14, 2019, 10:30 PM Jim Brain via cctalk <cctalk at classiccmp.org>
wrote:

> On 11/14/2019 11:05 PM, Brent Hilpert via cctalk wrote:
> >
> > (Without having gone through the code presented in full detail, but
> thinking from root premises.)
> >
> > ASCII A = 0x41 --> 2 bits on
> > ASCII T = 0x54 --> 3 bits on
>
> I agree, though I believe aT,At,AT,and at are all allowed, which
> complicates things a bit aT is the bad one, where the calc for 7E1 and
> 7S1/8N1 yield the same values...
>

1200 baud hayes modems required the initial AT be all upper case. I can't
recall if the 2400 baud modem relaxed this, or if it was later version.

Also, AT introduced commands. +++ could be followed immediately by ATH to
hang up...

But the parity trick discussed here matches my memory as well...

Warner

>