9 THE MINIMAL MONITOR
The minimal monitor is placed by the bootstrap loader starting at address 8000h. The monitor responds to two single-letter commands ’D’ and ’G’. The ’D’ command places the monitor in a download mode. Code in the Intel Hex format is expected. Code may be downloaded anywhere in the first 64L segment. The ’G’ (Go) command expects 4 hexadecimal characters. These 4 characters specify an address within the first 64K segment. A jump is performed to this address. If a user program is downloaded (using the ’D’ command), say at address 0C000h, then the GC000 command branches to the user program. In many cases, the user program is the application program or a monitor program, such as RMON167, and hence, the minimal monitor is no longer required. If, however, the user program wishes to return to the minimal monitor, it should branch to address 8000h. Note that the minimal monitor initializes the stack, so either a call or a jump to address 8000h would work.
The minimal monitor is a loop that executes the following flowchart:
