PC 232 Serial Ports Ports –Connectors at back of PC –Plus related internal electronics to send/receive PC 232 Serial Port –Follows EIA/TIA 232 standards

PC 232 Serial Ports: 9-Pin and 25-Pin Ports 9 pins or 25 pins Parallel ports have 25 holes Pins Holes 9-pin Serial Port 25-pin Serial Port 25-pin Parallel Port

232 Serial Ports: Send on One Pin Each Way 9-Pin 232 Serial Ports –PC sends on Pin 3 (modem receives) –PC receives on Pin 2 (modem sends) –Pin 5 is a signal ground defining zero volts PCModem

232 Serial Ports: Send on One Pin Each Way 9-Pin 232 Serial Ports –Other pins are control signals to tell other side when it may transmit –Or tell PC what modem is hearing on the line (ringing, modem carrier signal) PCModem

Serial and Parallel Transmission Serial: one wire, one bit per clock cycle* –Second (ground) wire needed for circuit is not shown 10 One Bit in Clock Cycle One Bit in Clock Cycle Two *For simplicity, we assume binary transmission (2 possible states/clock cycle)

Serial and Parallel Transmission Parallel –N bits per second on N wires –Parallel is faster than serial Eight Bits In Clock Cycle One Eight Bits In Clock Cycle Two

Serial and Parallel Transmission Parallel Transmission –N bits per second on N wires –N=8 in this example, but this is not the only possibility –N can also be 4, 16, 32, etc

Serial and Parallel Transmission Parallel Transmission is Only for Short Distances –Usually up to about 2 meters (6 feet) –Wire propagation speeds vary –Over long distances, bits from different clock cycles overlap

PC 232 Serial Ports: Voltages For sending data –One is -3 to -15 volts –Zero is +3 to +15 volts –Binary (only two possible states) +15v -15v 0 1 0

PC 232 Serial Ports PC 232 serial ports are binary because there are only two states (voltage levels) PC 232 serial ports are serial because data is sent on only one wire at a time These are separate things –One does not require the other