I'm adding a Max232, (or equivalent), type chip to a circuit, and thought I would stick a Pull Up or Pull Down resistor on the RS-232 Input line.
If there is no device connected to the RS-232 line, the resistor will hold the line at whatever level, and it won't float, or worse yet, bounce back and forth between High and Low.
I looked at the Max220-Max249 data sheet and it shows that there is an INTERNAL Pull Down to Ground resistor on the RS-232 inputs. Max220-249 Data Sheet
OK. So I don't need the resistor. BUT:
Why is the line pulled to Ground? Ground is an indeterminant state. Anything between -2 and +2 V is in no-mans-land, neither High nor Low.
Shouldn't the internal Pull Down, or my own external Pull down, tie to -5 V?