WHAT, exactly, is a hobbyist likely to gain from built-in debug features?

It is a significant advantage having those features, but, if he's trying to learn about the 805x series, he's already plowing up new ground, and learning the debug features and their use may not be as much an advantage to him as it is to an experienced user/programmer.

I'd guess he might just as well start with a "classic" 805x MCU with enough program store to accommodate an on-chip debugger, i.e. one with a built in line-by-line assembler and disassembler, so he can "play" with the features of the chip with his hands at the keyboard and "the bible" at his disposal. For that, I'd recommend Ultramon51, which ought to be pretty available at no cost. All he needs is a chip with 8kB of program store and a dumb terminal or PC with a serial port. Once he's learned something about the basics, he can then dig into the options provided by the JTAG debug port and a more advanced MCU.

The subject of these "small" chips has come up before, and the KEIL software goes out of its way to prevent the use of their demo package to program/debug them. Small chips are what the O/P was asking about, and I'm concerned that we're driving him off his intended course. I once suggested a way to circumvent this limitation in the KEIL demo software, one that, in no way, circumvents the code-size restriction, but you guys didn't like that. I won't describe it again in this forum.

RE