To demonstrate my HJS22 system on the VCF-E 2.0 in Munchen I needed an good demo program.
An running debug monitor would be a nice demo. First I modified an 6809 cross-assembler with the HJS22 instruction set.
Then I wrote the bootstrap and the debug-monitor program with this cross-assembler.
After power-up the bootstrap program is started. This small EPROM resident program transfers the monitor program
from EPROM to RAM location x'0200' and then control is passed to the monitor.
The Rx/Tx UART is written in HJS22 code. The Interrupt flipflop is used to transmit and the JIF is used receiving.
The debug-monitor commands are:D xxxx - display memory.
M xxxx - modify memory.
B xxxx - set breakpoint.
P xxxx - set user pgm PC.
R xxxx - run user program.
G - continue user program.
L - load user program.
S - user program status.
X - clear breakpoint.
C - clear memory.
Here is a "Hello World" program listing.