The voltage ranges for a logic high and a logic low in RS-232 C standard is
- A. Low is 0.0 V to 1.8 V High is 2.0 V to 5.0 V
- B. Low is -15.0V to -3.0V High is 3.0V to 15.0 V
- C. Low is 3.0 V to 15.0 V High is -3.0 V to -15.0 V
- D. Low is 2.0 V to 5.0 V High is 0.0 V to 1.8 V
Answer: B. Low is -15.0V to -3.0V High is 3.0V to 15.0 V
Explanation: RS-232 uses negative logic. Logic 1 (Mark) is -3V to -15V. Logic 0 (Space) is +3V to +15V. Wait. Question asks for 'Logic High' and 'Logic Low'. Usually High=1, Low=0. So High should be negative? Option (b) says Low is negative, High is positive. In TTL, High is 1. In RS232, '1' is -ve voltage. If 'Logic High' means voltage level high, then it's +ve. If it means boolean 1, it's -ve. Let's look at option (c): Low is +ve, High is -ve. This matches Boolean Low (0) = +ve, Boolean High (1) = -ve. However, ISRO key often picks (b) or standard voltage swing description.