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13. RS-232D Serial Interface Standard

1. The Mechanical Characteristics of the Interface
2. The Electrical Characteristics of the Interface
3. The Function of Each Signal
4. Subsets of the Signals for Certain Applications

The European version of RS-232D is defined in:

• V.24 - Mechanical Standard
• V.28 - Electrical Standard

13a. Mechanical Characteristics of the RS-232D

1. The connector is a DB25 connector. DB9 is not universally accepted.
2. The connector gender is Male at the DTE and Female at the DCE.
3. The assignments of signals to pins
4. The maximum cable length is 50 ft.
5. The maximum cable capacitance = 2500 pF. Typical cable has 50 pF/foot capacitance.

13b. Electrical Characteristics of the RS-232D

The transmitter side generates a voltage between +5 and +25 Volts for a Space (digital 0 or Low) and generates a voltage between -5 and -25 Volts for a Mark (digital 1 or High).

The transmitter voltage specification

The receiving side recognizes a Space (digital 0 or Low) as any voltage between +3 and +25V and a Mark (digital 1 or High) as any voltage between -3 and -25V. The standard allows for a voltage loss through the cable and noise immunity by reducing the receive requirements to +/-3 Volts!

The receiver voltage specification

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