HP 64793 Series User Manual page 22

Processing Commands
When a command is entered, the instructions from Exe_Cmd to
Cmd_A determine whether the command was "A", "B", or an invalid
command.
If the command input byte is "A" (ASCII 41 hex), execution is
transferred to the instructions at Cmd_A.
If the command input byte is "B" (ASCII 42 hex), execution is
transferred to the instructions at Cmd_B.
If the command input byte is neither "A" nor "B", an invalid command
has been entered, and execution is transferred to the instructions at
Cmd_I.
The instructions at Cmd_A, Cmd_B, and Cmd_I each load register
R3L with the length of the message to be displayed and register R4
with the starting location of the appropriate message. Then, execution
transfers to Write_Msg which writes the appropriate message to the
destination location, Msg_Dest.
Prior to writing the message, Clear_Old clears the destination area.
After the message is written, the program branches back to read the
next command.
The Destination Area
The "Data" section declares memory storage for the command input
byte, the destination area, and the stack area.
Getting Started 2-5