I have added the next version of monitor (v3).

This version has a big feature: you can debug your software via breakpoints and register alteration.

The whole breakpoint magic is done by RST 4 instruction. Monitor command X takes an address, save the value from this address and replace the original instruction by RST 4.

RST 4 led to breakpoint routine, which save all registers, including SP and PC, and returns to the monitor. You can see or alter values of all registers using the command R. After all, press C to continue program...

You can download Monitor v3 from GitHub. There is the source code as well as the bundled version with Tiny Basic (HEX or BIN). Enjoy.