The “Define Storage” directive reserves one or more memory locations. The label “P” allows the programmer to refer to the first location.
ORG $400 Start of program in memory
MOVE P,D0 Get an operand called "P" and put it in the D0 data register
MOVE Q,D1 Get an operand called "Q" and put it in the D1 data register
ADD D0,D1 Add the contents of data register D0 to D1 and put the result in D1
MOVE D1,R Put the result in memory location R
STOP #$2700 Stop program execution
ORG $1000 Start of data area
P DC.B $25 Reserve byte for P and initialize to $25
Q DC.B $37 Reserve byte for Q and initialize to $37
R DS.B 1 Reserve byte for R
END $400 End of program and code entry point
This assembler directive tells the assembler to call the next memory location “R”. This location is $1002. No data is stored.