Question 1

Within the DR DAS central system, how do you specify the modem configurations for individual stations?

Question 2

What modem initialization strings should be used at the central polling system?

Question 3

What settings are recommended for modems used with the EnvidasFW data logger?

Question 4

Where can I find information on modem commands?

1. Within the DR DAS central system, how do you specify the modem configurations for individual stations?
The DR DAS central communication program CommServ uses up to 10 modems for communications to remote stations. Within the central database each station is assigned to a communications Port. Using the Site Manager program communications parameters for Ports can be set.

By default communications setting for a station are defined by the Port to which it is assigned. The default setting for baud rate and modem initialization can be overridden in the Station Setup's Baud RATE: and INIT STR: fields.

2. What modem initialization strings should be used at the central polling system?
This is never a simple answer. It depends on the modems used at the central and the modems used at the stations. Ideally a network would standardize but in practice that often does not occur. For most modems the central modems will use
&f - to set a modem to the factory default
e0 - to turn off the echo back of commands to the PC
m0 - to turn off the annoying speaker
n0 - to force the modem to immediately connect at a fixed baud rate
s37 = x to set the baud rate: 9 = 9600, 8 = 4800, 6= 2400, 5 = 1200
If the modem does not support the n0s37=x commands, you can use &Nx, where
6=9600, 4=4800, 3=2400, 2=1200.

3. What settings are recommended for modems used with the EnvidasFW data logger?
On the Station Configuration form of the EnvidasFW setup select the Comm Port of the modem used for polling. Modem may be internal or external. Then enter a modem initialization string: at&fs0=1e0n0s37=9 is typical. This string sends the attention command "at", then the "&f" which sets the modem to factory defaults. This is so it will be in a known state. This example string then sends "s0=1" to have the modem answer on the first ring. It sends "e0" which turns command echo off.

To initialize the modem to only connect at one specific baud rate (9600) you would add "n0s37=9". This turns off auto detection and fixes the connection at 9600 baud. Other values for s37 are 8(4800), 6(2400) and 5(1200). If the modem does not support the n0s37=x commands, you can use &Nx, where 6=9600, 4=4800, 3=2400, 2=1200.

Note: it is tempting to just let the modems negotiate with each other to find the highest possible communication speed. But the station devices are set for a fixed baud rate so any higher rates used by the modems serve no benefit. In fact it takes much longer for the connection to be made and failures are more frequent when you do not fix the modem connect speed.

For modem communication you enter the modem communications time-out (in minutes) within the Timeout text box. For hourly data a value of 70 minutes is suggested. If after 70 minutes no communications has occurred on the port the modem is automatically reinitialized. If reinitialization fails repeatedly the EnvidasFW program will reboot the system. For internal modems this will also do a hard reset on the modem. For external modems power should be run through a relay that will open when the Envidas reboots, cycling power on the modem.

Enter 0 minutes if the connection is a leased line or direct serial cable. When 0 minutes is entered the initialization string is not sent.

4. Where can I find information on modem commands?
The best source of information for your modem will be found on the manufacturer's web site. General information information can be found at:
Basic AT Commands: http://webpages.charter.net/dperr/modem/atcmnds1.htm
S Register Commands: http://webpages.charter.net/dperr/modem/s_regs.htm