Memory and Addressing Modes Flashcards
what is the effective address
the address accessed by LDR or STR
Synatx for Immediate offset addressing
[Rn, #offset]
example of immediate offset addressing
LDR R0, [R1, #4]
LDR R0, [R1, #0]
Does immediate offset addressing change the value in the base register Rn
no
Syntax for register offset addressing
[Rn, Rm]
exmaple of register offset addressing
LDR R0, [R1, R2]
Advantage of register offset addressing
offset can be changed as program executes
does register offset addressing change the value in the base register
no
Syntax for scaled register offset
[Rn, Rm, LSL #2}
example of scaled register offset
LDR R0, [R1, R2, LSL #2}
When might scaled register offset be used
when offset is always 4x the count
in waht order does post index addressing work
- computes effecrive address and accesses memory
2. increments/decrements
example of post indexed addressing
LDR R4, [R1], #4
in what order does pre indexed addressing work
- increment/decrement
2. compute effective address and access memory
example of pre indexed addressing
LDR R4, [R1, #4]!
How can we tell immediate offset addressing from pre indexed addressing
the exclamation mark at the end
what does the exclamation mark do in addressing modes
permanently changes the address in the base register
can negative numbers be used in offset addressing
YES
