AT&T IPC-1600 manual Figure B-1 RS-232C Voltage Envelope

Voltage Envelope

The region between +3V and –3V is defined as the transition region and is considered an invalid level. A voltage more negative than –12V or more positive than +12V is also considered an invalid level.

During the transmission of data, the “marking” condition is used to denote the binary state “1” and the “spacing” condition is used to denote the binary state “0.” Figure B-1 shows the voltage envelope.

For interface control circuits, the function is “on” when the voltage is more positive than +3V with respect to the signal ground. The function is “off” when the voltage is more negative than –3V with respect to signal ground.

Invalid Level

+12V

Space (Binary 0)

+3V	Invalid Level
0V

-3V

Mark (Binary 1)

-12V

Invalid Level

Figure B-1: RS-232C Voltage Envelope

B-2 IPC-1600 USER’S GUIDE