"what is your doubt ?

the data so far indicates no need for pullups , the schematic shows none.

a pic pin when configured as output will never "float" its either high or low when set"


Hi Richard / Everyone - Thanks for your input. What you write makes total sense, I completely got the wrong end of the stick,
lack of knowledge on my part, so no pullups needed yet (bear with me, I think I will need one on the Rx though pulldown)

Tx first though:

Here is my simple Tx test code given no pullups needed, Tx driven directly by OUTPUT pin state.


'12F683'

ANSEL = %00000000 'Disable analog select so ports work as digital i/o
CMCON0 = %00000111 'Disable analog comparators
OPTION_REG.7=1 'Disable internal pull-ups

TRISIO = %00000000 'Set to OUTPUT
GPIO = %11111111 'Set all outputs HIGH to stop a false Tx

TestTx VAR BYTE

FOR TestTx = 1 TO 3 'Test transmit loop

LOW GPIO.4 'Pull Tx line LOW on transmitter to cause a Tx
PAUSE 50 'Wait for Tx
HIGH GPIO.4 'Stop Tx pull line HIGH
PAUSE 2500 'Wait 2.5 seconds

NEXT TestTx
END

So how does this look for basic a Tx test loop?

I'll post the Rx Data sheet and the reason given what Richard said above why I think I need a pulldown resistor later tonight.

Cheers David