The debugger in ROM (not present on the Macintosh 128, Macintosh 512, or Macintosh XL) recognizes the following commands:
PC [expr] (program counter)
Typing PC on a line by itself displays the program counter. Typing PC 50000 sets the program counter to $50000.
SM [address [number(s)]] (set memory)
Typing SM on a line by itself displays the next 96 bytes of memory. Typing SM 50000 will display memory starting at $50000. Typing SM 50000 4849 2054 6865 7265 2120 will set memory starting at $50000 to $4849... Subsequently hitting Return will increment the display a screen at a time.
DM [address] (display memory)
Typing DM on a line by itself displays the next 96 bytes of memory. Typing DM 50000 will display memory at $50000. Subsequently hitting Return will increment the display a screen at a time.
SR [expr] (status register)
Typing SR on a line by itself displays the status register. Typing SR 2004 sets the status register to $2004.
TD (total display)
Displays memory at the "magic" location $3FFC80, which contains the current values of the registers. The registers are displayed in the following order: D0-D7, A0-A7, PC, SR.
G [address] (go)
Executes instructions starting at address. If G is typed on a line by itself, execution begins at the address indicated by the program counter.
Note: If you want to exit to the shell, you just need to type: SM 0 A9F4, then G 0
Note: If you crash into the debugger and the system hangs, try turning off your modem.