Voltage Levels
It is helpful to understand what occurs to the voltage levels. When a MAX232 IC receives a TTL level to convert, it changes a TTL logic 0 to between +3 and +15 V, and changes TTL logic 1 to between -3 to -15 V, and vice versa for converting from RS232 to TTL. This can be confusing when you realize that the RS232 data transmission voltages at a certain logic state are opposite from the RS232 control line voltages at the same logic state. To clarify the matter, see the table below. For more information, see RS-232 voltage levels.
| RS232 line type and logic level | RS232 voltage | TTL voltage to/from MAX232 |
|---|---|---|
| Data transmission (Rx/Tx) logic 0 | +3 V to +15 V | 0 V |
| Data transmission (Rx/Tx) logic 1 | -3 V to -15 V | 5 V |
| Control signals (RTS/CTS/DTR/DSR) logic 0 | -3 V to -15 V | 5 V |
| Control signals kjnic 1 | +3 V to +15 V | 0 V |
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