Re: Caddx/Ademco Downloading

["Al Mundy" <t2e4@xxxxxxxxxxx>]

Mark Leuck wrote:
> Correct, alarm panels communicate between 100 baud to 300 baud depending on
> the panel

the hayes commands also let you set the DTE (equipment) communication
speed. Well, not set it, but let it auto discover what the rate is. I
believe it's \J or \J0

I'm not trying to argue, by the way, just trying to save you all some
money next time you need one.

To quote from
http://en.wikibooks.org/wiki/Serial_Programming:Modems_and_AT_Commands

An issue which can be very confusing is the difference between the line
speed (the data transfer speed on the telephone line) and the speed on
the serial line between the DTE (computer) and the DCE (modem).

First, there is always some general confusion about the line speed,
because some line speed is given with taking compression into account,
while other data is given without taking compression into account.
Also, there is a difference between bps and Baud due to the modulation
schema used on the line. In addition, marketing blurbs obscure the
picture. We will not make any attempt to clean up the long-standing
Baud vs. bps confusion here (it is hopeless :-)). It is just
recommended that whenever the modem returns information about line
speed the above mentioned differences are taken into account to avoid
any misinterpretation.

Second, the speed on the telephone line does not necessarily have to be
the same as the speed on the serial line. In fact, it usually isn't on
modern modems. It is recommended to set the DTE/DCE speed to a fixed
speed instead of following the line speed. Logically, the fixed DTE/DCE
speed should be large enough to cope with the highest expected line
speed. V.90 modems should e.g. be accessed via 115200 bps or higher on
the serial interface.

Setting the DTE/DCE speed on modern modems is quite simple. They all
use autosensing on the serial interface. That is, they themselves
detect the speed of data as received from the DTE and use the same
speed to return data to the computer. They usually also autosense the
parity, and 7 bit / 8 bit data length. Usually modems assume one stop
bit when autosensing the serial interface.

When a modem sets up a connection with a remote party it can report the
used speed. In fact, it can report the line speed or just the DTE speed
(some modems can report both). The end user is most probably interested
in the line speed, and not the DTE/DCE speed. So from this point of
view, it is best to set the modem to report the line speed, and e.g.
write the received information to a log file. However, some old
communication software or modem drivers interpret the response from the
modem as a request to change the DTE/DCE speed. In such cases the modem
must be set to always return the DTE/DCE speed. Since this DTE/DCE
speed will be the same as detected via autosensing there will be no
speed change.

In the rare case that the DTE/DCE speed should indeed follow the line
speed, the responses from the modem should of course be set to return
the line speed. Then the DTE software has to evaluate the response, and
change the DTE/DCE speed accordingly. This is really not recommended
these days.

See the #W: Negotiation Progress Message Selection command for details
on how to set which response to get.


Note: Some modem manufacturers call the DTE/DCE speed DTE speed, and
the line speed DCE speed. Others distinguish between DTE speed (DTE/DCE
speed on the serial interface), DCE speed (bps between the modems), and
line speed (Baud rate between the modems).

-----





> "Roland" <roland@xxxxxxxxxxxx> wrote in message
> news:blZfh.42497$qp1.16086@xxxxxxxxxxxxxxxxxxxxxxx
> > I think it is the harware in the alarm panel that is the bottle neck to
> > download speeds, not any modem seting.
> > "Al Mundy" <t2e4@xxxxxxxxxxx> wrote in message
> > news:1166040451.140324.288510@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > >
> > > Roland Moore wrote:
> > >> New internal modems cost l0 bucks or less now days. Too bad the
> > >> manufacturers  won't design a panel with a communications chip that
> will
> > >> go
> > >> up to 56K (33.6K) and that can talk to the cheap modems.
> > >
> > > Well, IIRC, any modem that uses the hayes command set can be limited to
> > > a max connect speed.
> > >
> > > In fact, I looked it up, and  ATN0 will tell the modem to only
> > > handshake at the speed set in register 37, so in theory,
> > >
> > > ATS37=1200
> > > ATN0
> > >
> > > Should set the max speed to 1200   Anyone have an external
> > > hayes-compatible and a alarm panel to play with?
> > >
> > > Memory tells me the hayes 1200 / 2400 cost about $80 14 years ago.
> > > Certainly they should be worth no more than $10 now. After all, who
> > > buys them?  Alarm installers?
> > >
> > >
> > > If you really need one bad, I would suggest going to a local company,
> > > if you can find one that seldom throws stuff out, and ask.  Governments
> > > (who have rules about tossing stuff) and charities might be good
> > > choices.  I'll keep an eye on the goodwill stores around here.
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >> "Mark Leuck" <m..leuck@xxxxxxxxxxx> wrote in message
> > >> news:asSdnaQbWbSl7-LYnZ2dnUVZ_q-vnZ2d@xxxxxxxxxxxxxx
> > >> >
> > >> > "Roland" <roland@xxxxxxxxxxxx> wrote in message
> > >> > news:hsJfh.8951$GB1.2096@xxxxxxxxxxxxxxxxxxxxxxx
> > >> >> I just get sick now when I see the prices for them.
> > >> >>
> > >> >
> > >> > How so? Even worst case price from Ebay is $60-$70, when those modems
> > >> > were
> > >> > new they went for $1,000 to $1,200
> > >> >
> > >> >
> > >
> >
> >