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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
0V
Invalid Level
-3V
Mark (Binary 1)
-12V
Invalid Level
Figure B-1: RS-232C Voltage Envelope
B-2 IPC-1600 USER’S GUIDE