No secret, anyone with a scope or logic analyser could work it out!
4800,n,8,1
This is relatively slow by modern standards but was a good compromise between speed, processing time between bytes (to actually save the downloaded data), and what the early original PICAXE (4MHz) devices could keep up with reliably.
After each byte is downloaded it is echoed back to the computer so that the computer can verify each byte was reliably received.