Lc3 Assembly notes

LEA

Load the address (not the value) of a Label

LEA R0,Label1 ; Load the address of Label1

Label:

When you put a label, the label point to a memory address, The Label is pc offset, you can treat it a as memory address.

LD

Load the value from a label (addres)

LD R1, Label1 ; Load the value stored in Label1 address to R1

ST R2, Label1 ; Store the value of R1 into the address Label1

LDR

Load the value from a address, and the address is from a Register

LDR R1,R2,#0, Load the value from the memory where the R2's value pointing to

LD can be rewrite with LDR

For example

LD R1, Label1

=

LEA R2， Label1 ;store Label1's address to R2

LDR R1, R2, #0 ; Load Label1's value

ST and STR is similar to LD, and LDR

JSR is use to call function

Need to save and restore R7 to a label, then RET can work.

BRnzp ; Branch if last accessed register is negative, zero or positive (uncondition)

BRz ; Branch if last accessed register is zero.

BRzp ; Branch if last accessed register is zero or positive

for example

BRp Label2

.FILL

Assign a address to Label, reverse the address to this label, and initial the value

NINE .FILL ＃57

Allocate a memory address to NINE, and fill that address with the value 57

ZERO. FILL x0000


NAME    .STRINGZ "hello"

Allocate a address to NAME, and fill the memory with h e l l o , chars.

ARR .BLKW 20 ; assign a address to ARR, and reserve the following 20 address for it.

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Feng