SERIN pin can be tied low to GND? or pulldown resistor preferred??


Senior Member
Hi All,

I've seen a few comments around the web that say the picaxe SERIN pin can be tied to GND to ensure the picaxe operates efficiently and doesn't randomly reboot or pause etc. (assuming the project has no further need to be re-programmed).

In all my projects, i've simply replaced the typical 10k/22k resistors on the SERIN jack, with a single 33k pulldown resistor to keep the picaxe running fine and it works perfectly everytime. (i do this after i have no further need to program the picaxe in my final projects).

So, has it been proven that the SERIN pin can safely be tied directly to GND and not use a pulldown 33k resistor at all???

Thanks in advance.


Senior Member
I don't remember having seen a recommendation on not using a resistor to tie down the SerialIn pin. I always use a 10K resistor when tying SerialIn pin low. It has the advantage of being able to reprogram the chip in-circuit in case you need too.


Senior Member
I always use something around 10k / whatever I have to hand.
As serin pin is input only, then tying to ground wont do any harm, of course you will not be able to in cct program.


Technical Support
Staff member
The potential risk is that an adverse event could cause the SERIN pin to become an output high and, if shorted to 0V, could draw excess current through that pin, destroy the pin, port or perhaps the entire chip.

Despite that risk being extremely low, the recommendation would be to use a pull-down resistor than a hard connection to 0V just in case it ever does happen. I recall 1K to 33K is what's usually recommended.

If one is prepared to live with the adverse risk and consequences for a non-commercial home project then shorting to 0V is probably acceptable but a resistor is likely just as easy to fit as a wire link and not much more costly.


I have used a 100 kOhm pull down resistor and may have 3 pin socket where a programming connection such as the AXE029 can be plugged in without problems.