PICAXE serial download pin resistors

Hi everyone

Can someone please explain the purpose of the 22k/10k resistors on the Rx programming pin of the PICAXE.

My reason for asking is that I will be driving this pin with an invertor (CMOS compatible schmitt) that will connect to a RS232/USB IC (FT232RL) and not to a AXE027 USB cable for programming purposes.

thanks

The 22k is to protect the input from voltages higher than Vcc which can be applied if using a "traditional" serial port.
The 10k is to hold the pin low when the download cable is not connected.

If you are supplying a signal from a device where the output is the same as the PICAXE supply rail voltage and can swing both high and low, then you don't need the resistors.

Thanks BeanieBots. That's what I expected.

Your quick reply is greatly appreciated

You'll want to keep the serin pin pulled down somehow... If it floats, you can get unexpected resets.

To amplify slightly, if your (working) ttl-level (or picaxe supply rail voltage level) programming cable is disconnected, then you are no longer using it to pull down the serin pin, so it would float and cause resets. If the programming cable would never be disconnected (and the device it's plugged into is never powered down) then you wouldn't need an on-board pull-down. For the tiny cost in board space, most would recommend that you include the resistor to increase flexibility.