Active low transmitter question

[LEDave]

Hi Ioannis - Looking back at the thread I've done a pretty miserable job of it so far certainly information wise and I apologise to everyone.

*I think it would be best to have the Data sheet of the that transmitter.* For sure, I'll add a screen shot then a full data sheet if needed.

I intend to use maybe a 12F683 to pull a Transmitter Input pin LOW for a few m/s to make it transmit then hold the Tx pin high to stop false triggering via floating voltages if this is safe to do this without damaging the transmitter or pic. I'll add some code as soon as possible, here's the screenshot:

[richard]

I intend to use maybe a 12F683 to pull a Transmitter Input pin LOW for a few m/s to make it transmit then hold the Tx pin high to stop false triggering via floating voltages if this is safe to do this without damaging the transmitter or pic

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

[LEDave]

"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

[LEDave]

Here's the Rx schematic. When an Rx is received it outputs 5v onto the corresponding pin, which will then be read by the pic.

My question now is (and this should have been the question all along):

On the 12F683 pic I need to set a Tris pin to INPUT and read the pin for state change from LOW to High as the Rx is received.

TRISIO = %00000001 'Set to Input

TestRx 'LABEL
Do SomeThing 'LABEL

TestRx
IF
GPIO.0 = 0 THEN TestRx 'Nothing has happened continue to loop and check for state change

IF

GPIO.0 = 1 then DoSomeThing

DoSomeThing

Set alarm off in this case........

So, here's the $64k question from me: How do I hold GPIO.0 LOW until a 5v Rx is received? Is it a pulldown resistor?