Application Note 003

MODEM configuration for FF-800 remote terminal access

IN THIS AP-NOTE:

MODEM set-up
Call-back capability
Special considerations

MODEM SET-UP

When using a modem to gain access to the FF-800 there are some configuration issues that the user must address before connecting the modem to the FF-800.

The first issue regards the modem set-up:

Connect the modem to your computer or terminal with an appropriate modem cable. If you are using a computer, run a suitable terminal program (such as PROCOMM, or an equivalent).

Issue the following "AT" style commands:

ATE0			disable the modem character echo
ATQ1			disable modem command responses
AT&W			save configuration to non-volitile memory

disconnect the modem from the computer or terminal.

The modem is now ready to connect to the FF-800. It should be noted that a modem configured as such will look "dead" when connected to a terminal. Since the echo and command responses are off, there is basically no response to commands -- however, commands should still execute. The "ATS0=1" command should light the "AA" light and allow the modem to answer incomming calls.

It should be noted that the "auto log-off" commands ("NO" and "+++NO" are duplicate log-off command keywords that are designed to allow the FF-800 to log-off when the modem hangs up) for the FF-800 will not work with the modem configured as above. Therefore, the user should take extra care to log-off (using the "LOGOFF" command) before disconnecting the modem. Failure to do so will result in your FF-800 remaining un-locked which could allow a "hacker" to gain easy access to your system.

After setting up the modem, there are some parameters on the FF-800 that might require some pre-installation configuration (although each of the following parameters comes with a factory default, the user may wish to change the setting(s) to meet the special needs of their application).

Be sure to set the connect type to modem or TNC (serial terminal command "SCIC 1" = modem; "SCIC 2" = TNC). The modem initialize string will not be sent unless this parameter is set to modem or TNC. Use the modem mode (SCIC = 1) if the modem shares the same phone line as the FF-800 patch, and use the TNC mode (SCIC = 2) if you use a TNC or a modem on a separate line.

Special note for TNC users:

For firmware V2.14 and above, a "DUPLEX" command has been added that allows the FF-800 to disable character echo. This was done primarily for TNC users to keep the TNC from returning a message containing the echo of your previous message (which is redundant in the TNC mode and causes the throughput on the TNC channel to be reduced). If you are using a TNC, you should enter "DUPLEX 0" on the serial port to disable the echo.

Be sure to set the modem control strings to meet any special system requirements.

The following descriptions highlight each of the modem string commands:

Escape code: The escape code corresponds to the character that the modem (or TNC) uses to enter command mode when connected. The Hayes style default is the "+" character, but this may be changed on the modem if desired, so this command was included to allow the FF-800 to adapt do differing modem configurations. The escape code is entered into the following strings by pressing the <esc> key (ASCII 27 decimal) once. This tells the FF-800 to send three (3) of the "escape" characters.
Delay character: This character tells the FF-800 to delay 3 seconds when used in the modem control strings. It is entered by pressing the <cntl>-D combination (ASCII 04 decimal).
NOTE: The <esc> and <cntl>-D characters do not print when they are typed, however, the FF-800 prints "<esc>" and "<delay>" when displaying the contents of the respective string. Also, if you backspace/delete one of these characters, the cursor will not move (indicating that an "invisible" character was just deleted).
Modem initialization: The modem initialization string is sent by the FF-800 whenever it is reset IF SCIC = 1 or 2. This feature allows the modem to be placed in a particular state when the system is powered-up or reset. The default string is "<esc> <delay> ATS0=0H". Another string may be used to reset the modem "<esc> <delay> ATZ" or whatever the user desires.
DCEUP/DCEDN: This pair of strings is associated with the DTMF command Modem Control {(cnfg)535} which allows the modem to be placed on or off line by DTMF command. DCEUP corresponds to (cnfg)5351 and defaults with "ATS0=1" -- this places the modem in auto-answer mode and allows remote connections. The DCEDN string corresponds to (cnfg)5350 and defaults with "ATS0=0" -- this prevents the modem from answering. This set of commands is useful because it allows on-demand access without leaving the modem on-line and vunerable to hacking. It is also useful when the modem and autopatch share the same phone line because it allows control autopatches to ocurr except when modem access is desired.
DCECON: This string is associated with the DTMF command, Modem On Line. As described in chapter 5 of the FF-800 manual, this command was designed to allow the user to connect to the modem from a control autopatch (see chapter 5 for a detailed description of this feature). It defaults with "ATA".

CALL-BACK Capability

The DCEUP/DCEDN and DCECON strings and commands can also be used to construct a "call back" feature that allows the modem to call a particular number as the result of a DTMF command (or macro). This can provide additional security or provide access to a modem where there is dial-out but not dial-in capability. Using these controls, up to three phone numbers may be programmed for call-back. Each of the DCEUP/DCEDN/DCECON strings may contain one dial back number and that number would be activated by the appropriate DTMF command. An example of such a string follows:

>DCECON ATDT9,3684329
Modem CONNECT string: ATDT9,3683716
>

The user would use the "01536" command to initiate the dial sequence for this string. If the modem shares the same phone line as the FF-800 patch, the you should be aware that this command won't work from a control patch because there is no provision for hanging up the FF-800 control patch before issuing the dial command. Therefore, this feature will only work where there is a separate line or the commands must be entered via a receiver port.

Remember, the strings are limited to 15 characters. A future upgrade is planned to allow a list of call back numbers to be maintained that will formalize this feature and provide some additional capabilities. However, no date is available as yet for release of this feature.

Special considerations

To properly use the modem escape code in any of the previous strings, the following sequence should be used:

"<delay> <esc> <delay>"

This sequence meets the Hayes style escape code requirements -- using the "<esc> <delay>" sequence will generally work, but it may fail under some circumstances because it doesn't guarantee the leading guard time required before the begining of the escape character sequence.

Most users who connect a modem have reported few difficulties and many have simply used the default settings for the FF-800. However, one user has used the DCECON string/command to allow the modem to be brought off-line while the user is logged onto the modem. This was done with the following string setting: "<delay> <esc> <delay> ATS0=0O". This string disables the auto-answer and returns the modem to the connect mode (so that you can still issue serial commands until you hang-up). To disable auto-answer, the user issues "CRX 01536" and waits for about six seconds. More commands may be entered, until the user hangs-up the modem. This feature requires that the modem be configured as described earlier in this document.