Dumb serial question

Ugha

This is really a dumb question... I should know this.

When using serial communications... do you need a pullup or pulldown resistor to
keep it from floating? If so, which and what size?

Mike Green

The heart of the matter is that a serial communications line is idle at the logic 1 state. The logic 0 state is used for the start bit. For a logic level line, +V is logic 1 and 0V is logic 0 where V is typically 3.3V or 5V. RS232 uses -V for logic 1 and +V for logic 0 where V may vary from 3V to as much as 15V. If you have a logic level serial line, you want a pullup to keep the line in idle state. If you have an RS232 level serial line, you want a pulldown, preferably to a negative voltage.

Ugha

It's a +5v logic 1 serial device... a pullup... thanks Mike... this should make it so i get less "trash" data [noparse]:)[/noparse]