Active low transmitter question

[mpgmike]

If your question is, "Can the PIC safely overcome the 10k pull-up resistor?", the answer is absolutely yes. Again, will it do what you want, you'll just have to try it and see.

[LEDave]

Thanks for your help mpgmike, anyone else have any thoughts on this?

[richard]

anyone else have any thoughts on this?

using a resistor to drive a pin to a default logic level is not an uncommon practice.
so common that i would not be surprised that your [type not disclosed ] transmitter has such a pullup
resistor already installed. the only reason i could see for an additional pullup would be if the pic was routinely disconnected
from a device that did not have a built in pullup or that an open drain/collector pic pin was in use.
summing up with the detail[almost non existent] you have provided it seems to be a pointless waste of a component
that could easily be eliminated with good programming practice.

[Ioannis]

I think it would be best to have the Data sheet of the that transmitter.

Ioannis

[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