I forgot to mention that there is another special software command, I think is for debugging purposes, it downloads code to RAM (from 0x600), does integrity check then jumps to your code which executes it. It works on the VER.4.04 boot loader.
I've included a HEW project with the sample code that sets port P8_0 to high for you.
It also contains the required code to pass the boot loader integrity check.
If it works on VER.1.00 you should see the LED constantly lit.
I've added 3 files to:
https://github.com/truhy/m16c-flasher/tree/main/Sourcecode/Release"boot_dl_P8_0 source code - HEW project.zip" = source code of below
"boot_dl_p8_0.bin" = program to be uploaded into RAM
"upload to ram - p8_0.cmd"
The files are prepared and ready to go, simply edit the batch file "upload to ram - p8_0.cmd" with your COM port and try.
If you want to modify and recompile the test code:
Note, as you've found out already, since HEW was made in the past the workspace and project files (plain text files) stores absolute paths and needs correcting (find and replace).
There is another small problem, unfortunately my tool supports only input binary file so I have included srec_cat with a batch file to convert motorola into binary, but it also fills in zeroes before 0x600 so you will need to remove them.