int e l CHAPTER 13 Mapping User Code Memory You might have noticed by now that some of external CODE memory locations that MCS BASIC-52 calls and uses are located around 2000H and some of the locations are located around 4000H. Specifically, they are as follows: LOCATION FUNCTION 2001 H ON RESET, MCS BASIC-52 LOOKS FOR A 0AAH IN THIS LOCATION, IF PRESENT, CALLS LOCATION 2090H 2002 H MCS BASIC-52 EXAMINES THIS LOCATION TO SEE IF THE USER WANTS TO IMPLEMENT THE COMMAND/STATEMENT EXTENSION OPTION, A 05AH IS TO BE PLACED IN THIS LOCATION TO EVOKE THE COMMAND/EXTENSION OPTION 2048 H MCS BASIC-52 CALLS THE LOCATION IF THE USER WANTS TO IMPLEMENT THE COMMAND/STATEMENT EXTENSION OPTION.
THE USER WILL USUALLY SET BIT 45 THEN RETURN. 2070 H MCS BASIC-52 CALLS THIS LOCATION TO GET THE USER VECTOR TABLE ADDRESS WHEN THE COMMAND/STATEMENT EXTENSION OPTION IS EVOKED. THE ADDRESS OF THE VECTOR TABLE IS PUT IN THE DPTR BY THE USER. 2078 H MCS BASIC-52 CALLS THIS LOCATION TO GET THE USER LOOKUP TABLE ADDRESS WHEN THE COMMAND/STATEMENT EXTENSION OPTION IS EVOKED. THE ADDRESS OF THE LOOKUP TABLE IS PUT IN THE DPTR BY THE USER.
2090 H MCS BASIC-52 CALLS THIS LOCATION WHEN THE USER EVOKES THE ASSEMBLY LANGUAGE RESET OPTION 4003 H EXTERNAL INTERRUPT 0 400B H TIMER0 INTERRUPT 4013 H EXTERNAL INTERRUPT 1 401B H TIMER1 INTERRUPT 4023 H SERIAL PORT INTERRUPT 402B H TIMER 2 INTERRUPT 4030 H USER CONSOLE OUTPUT 4033 H USER CONSOLE INPUT 4036 H USER CONSOLE STATUS 403C H USER PRINT@ OR LIST@ VECTOR 4100 H -41FF H USER CALLS FROM 0 TO 7FH - 159 -