Serial port data pin

[Michael]

Do the serial port data pins (rcv and xmt) have an internal pullup on them
inside the PC?

If I lose the hardwire connection, does it still have a voltage on the pin?


I'm primarily concerned with the receive data pin.

Just thought I'd ask for a quick answer -- I'm sure I could google it.

THANKS.

[Archangel]

If you use the UART then you must use a pull up resistor. If you are using a software serial routine, the idle state is as follows Low for Inverted and High for True. Use pull up or pull downs as needed. It is never good practice to allow an input to float.

[Michael]

Yeah -- I know and I'm the sure the answer is yes -- was just being extra sure.

But I'm interested in the PC itself -- not the peripheral device (PIC etc).

Take away the hardwire and do you see a pullup voltage INSIDE the PC on
the data pins?

[mackrackit]

Have you looked at the data sheet of your PIC.

[Michael]

nevermind -- answer is yes as I suspected.

PIC datasheet?

"inside the PC" -- "not the pic"