AT Z S46=0 &Q0 &D2 AT Z H0 Line 1 is the initialization string, which needs to set the modem to 9600 baud, no compression, and no error correction protocol. Line 2 is the shutdown string, which should hang up the line (if dropping DTR hasn't already) and reset any parameters you like. Settings known to work: Practical Peripherals 14400FX V.32bis AT Z S46=0 &Q0 &D2 AT Z H0