Unpredictable problems may occur if the modem initialization is interrupted by the next incoming call.


Here is an example:

With the S0 register greater than 0 the modem will auto answer. If a command is issued to the modem to configure it and the modem recieves a call, it will character abort the call. Often the fax software won't understand this and get lost and the incoming call is hung up on.

It was found that the same problems could occur if a DID call was received after the completion of a call on the POTS line but before the application had completed initializing the modem.


Firmware version 1.28D or greater fixes this problem. This firmware applies a busy out rule (time and function) on the completion of a POTS call just as they are applied on the completion of a DID call. The firmware can be downloaded from our site at:


Using the (*DW) command an application can setup the DID modem to busy out the line after the completion of a call. This allows the application to initialize the modem without being interrupted by the next incoming call.

Command: *DW Busy-Out Timer at End of Call
Values: 0-255
Default: 0
Description: This command defines the amount of time to busy out the modem upon disconnecting from a call. The delay is ended when the timer runs out or a *DS command is received.

*DW0 This command disables the delay. It ends the delay, but it also places the line a busy-out state.

*DW255 This command will extend the delay indefinitely.

The line is busied out in the following cases:

- Modem is set to the factory default start format *DS0

- Modem receives an incoming ring on the POTS line

- Modem is given the dial command ATD

- Modem is set with the *DW command to busy-out delay after finishing a call