Serial Output logic inversion?

[MikeMl]

I used to know this, but I have forgotten.

To connect the serial output (TX) from a PIC that has a USART to the SerialDataIn Pin of a computer's serial port requires a logic inversion, right? That is normally provided in a MAX232, which also provides negative level shift.

AFAICR, I have done this before with nothing but a simple inverter operating between 0V and 5V. I know that the RS232 spec expects the logic level to swing below 0V, but it seems to work ok even if it doesn't.

 

[Mr RB]

Yes it needs to be inverted.

If you need a hardware inverter solution you can use a NPN transistor (as open-collector) with a pullup resistor on it's collector.

 

[Pommie]

Mike K8LH posted a simple version a while ago. Clicky.

Mike.