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+4 votes

The voltage ranges for a logic high and a logic low in RS-$232$ C standard is

  1. Low is $0.0 V$ to $1.8 V$,  High is $2.0 V$ to $5.0 V$
  2. Low is $-15.0 V$ to $-3.0 V$,  High is $3.0 V$ to $15.0 V$
  3. Low is $3.0 V$ to $15.0 V$,  High is $-3.0 V$ to $-15.0 V$
  4. Low is $2.0 V$ to $5.0 V$,  High is $0.0 V$ to $1.8 V$
in Non GATE by Boss (30.8k points) | 1.8k views

2 Answers

+4 votes
Best answer

ans is (c)

The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels for the data transmission and the control signal lines. Valid signals are either in the range of +3 to +15 volts or the range −3 to −15 volts

by Active (4.9k points)
selected by
It should be B

because -15 to -3 is less than +3 to +15 ?
+2 votes
by (31 points)
I think answer is Option C

Check in Wikipedia
This link seems to support the option c.  Under the heading 'Voltages',

"A high bit, or mark state is identified by a negative voltage and a low bit or space state uses a positive value. This might be a bit confusing, because in normal circumstances, high logical values are defined by high voltages also."

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