Modem acronym for modulator-demodulator converts a series of binary voltage pulses into an analog signal the receiving modem translates the analog signal back into digital data

Date Flow: Simplex only transmit in one direction One way Monitor Computer

Data Flow: Half Duplex data may travel in both directions, but only in one direction at a time non-simultaneous two-way communication computers use control signals to negotiate when to send and when to receive

Half Duplex

Data Flow: Full Duplex complete two-way simultaneous transmission faster than half-duplex communication because no turnaround time is needed

RS-232C Used for connections between computer and modems, among other things 25-pin connector with a specific arrangement of leads computer usually has male DB25 connectors while modems are female In practice, fewer than 25 wires are generally used in applications

RS-232 DB-25 Connectors DB-25 Female DB-25 Male

RS-232 DB-25 Pinouts

RS-232 DB-9 Connectors Limited RS-232

MODEM COMMANDS MEMORIZE THESE! AT- PROCEDES ALL MODEM COMMANDS ATDT- DIAL PHONE # USING TOUCH TONE ATDP- DIAL PHONE # USING PULSE DIALING ATA- ANSWER AN INCOMING CALL ATHO- HANG UP IMMEDIATELY AT&F- RESET MODEM TO FACTORY SETTING ATZ- RESET TO POWER UP SETTINGS *70- CANCEL CALL WAITING