> Although I have used Putty and TeraTerm properly configured, the <CTRL><M> key combination, which is supposed to correspond to <CR> or 0x0D in these terminal emulators, does not allow me to activate command line mode. It is presenting messages out of control, as I indicated above.

I think in a case like this, where one can modify the source and rebuild, I might change the specific test for the 0x0D character to a printable one: pick any letter. See if that works. Then figure out what's happening with a control character input. Perhaps get the software to echo its inputs back, in hex?

Thank you for giving me that hope GARTHWILSON, but while that happens .....

The only thing I have achieved is that the debugger/monitor attends to a Break launched from TeraTerm, as can be seen below:
..........................
0.1FF 0.FFF9 00 x00 y00 NV-BDIZC H>
0.1FF 0.FFF8 00 x00 y00 NV-BDIZC H>
0.1FF 0.FFF7 00 x00 y00 NV-BDIZC H>
0.1FF
Terminal break signal detected

0.1FF 0.FFF1 00 x00 y00 NV-BDIZC H>
0.1FF 0.FFF0 00 x00 y00 NV-BDIZC H>
..................

But nothing I have achieved regarding entering command line mode. For now I'm taking a break waiting for a kind soul want to help me. :-])