Application Note 003

MODEM configuration for FF-800 remote terminal access



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:

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:

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

The following descriptions highlight each of the modem string commands:

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.