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PC 232 Serial Ports

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. 9-pin Serial Port.

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PC 232 Serial Ports

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  1. 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

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

  3. 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 PC Modem

  4. 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) PC Modem

  5. Serial and Parallel Transmission • Serial: one wire, one bit per clock cycle* • Second (ground) wire needed for circuit is not shown 1 0 One Bit in Clock Cycle One One Bit in Clock Cycle Two *For simplicity, we assume binary transmission (2 possible states/clock cycle)

  6. Serial and Parallel Transmission • Parallel • N bits per second on N wires • Parallel is faster than serial 1 1 1 1 0 0 Eight Bits In Clock Cycle One Eight Bits In Clock Cycle Two 1 1 1 1 0 0 0 0 0 0

  7. 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. 1 1 1 1 0 0 1 1 1 1 0 0 0 0 0 0

  8. 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 1 1 1 1 0 0 1 1 1 1 0 0 0 0 0 0

  9. 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 0 0 1 -15v

  10. 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

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