Waaat? You never heard of it before? If so, please do take the opportunity to educate yourself at www.picaxe.com.
As I stated elsewhere:
My little experiment is a success! I doubled the value of the resistor going to ground on that voltage divider on the the serial in of the Picaxe to prevent going over the maximum current sourcing limit (provides positive current) on the 74LS04 output pin driving that serial in signal. It worked flawlessly for the small program file I loaded. No surprise on what the code does - it blinks a LED on and off in an endless loop.
system functional check 11am 09/13/2019