User's Manual

4.11. Serial Data Flow Control
If large amounts of data will be sent with the FireLine, and the serial port is
operated at a faster data rate than the over-the-air rate, it may be possible to
overflow the internal data buffer. To ensure the transmit buffer does not
overflow, enable and use hardware flow control. Hardware flow control is
enabled with the ATCH 1 command. Note that the FireLine modem will
always indicate the status of its internal buffer using the CTS signal on the
DB-9 serial connector. When CTS is negated, the internal buffers are more
than 80% full. When it is asserted and it is “Clear to Send”, the buffers are
less than 80% full.