You can do exactly the same via JTAG; in fact better, because the JTAG can write the code direct to code memory - without involving the 8051 at all, and without you having to type the code line-by-line at your VT100 using a crude inline assembler.

The JTAG can directly access the peripherals - without the 8051 having to interpret your commands, execute code to access the peripheral, and then execute more code to pass the results back to you.


I use the Triscend devices with JTAG etc; this can download over 60K of code in only a few seconds - I'd hate to have to do that on a line-by-line assembler, with no symbolic addressing, etc.


Because it has to run in the 8051, you're restricted to a line-by-line assembler without symbolic addressing; All you can see is raw hex data, etc, etc.

JTAG makes no demands on the 8051 whatsoever; it just gives you direct access to registers, peripherals, memory - everything.
You can then use the power of a PC to give you a full-function assembler, high-level language source debugging, symbolic display, etc, etc, etc.


Having used both resident debugger/monitors (including MS-DOS DEBUG) and JTAG-based solutions, I have absolutely no doubt that the JTAG-based solutions are by far the most convenient & capable.