Hooked up with a terminal emulation program and RX/TX to the badge, correct baud/parity/len and RAW mode and display binary, we should see the first part of header being produced (I only keyed in that part of the program.)

Testing with ASCII HEX

0400 generates two bytes saying we have 4 bytes, ie two instructions when they have been padded
012 nonsense instructions, but choosen to verify correct Hex conversion
AF0
. EOT marker.
This is of course put as a single line "0400012AF0."

But I am saddled with the serial bug, I must enter one character on the keyboard when I see the badge code is looping for the next input character. I can enter 3 characters at a time (after the initial 4), without Input/Output serial clash.

Sigh... so many errors. Some simple typos, offsets wrong, some stupid logic.

The output routine was rewritten to buffer a half-byte to avoid using the Serial for output too soon. The checksum needed to include the length byte. Byte ordering in the output corrected.

Entering the nonsense 2 instructions from above and then using built in "Save program to serial" I get the same output, as my program. Yeah!

But that was a coincidence.....