1. LA Load Address

2. LA Instruction type: RX Explicit Coding: B1,D2(X2,B2)
Example LA ,3(4,5)
Example LA ,TABLE(7)
Use: Creates an address (operand 2) which is loaded into the operand 1 register

3. What does it do? LA 8,Y R8 00 12 3D 8A (Before) R8 00 00 10 04 (After)
Memory F1 F2 F3 F4 F5 F6 F7 F8 F9
Address X’1000’ Y

4. What does it do? LA 8,Y(9) R8 00 12 3D 8A R9 00 00 00 04 R8
(Before) R8
D 8A R9 R8
(After)
Memory F1 F2 F3 F4 F5 F6 F7 F8 F9
Address X’1000’ Y

5. What does it do?
LA 7,5(8,9)
(Before) R8 R9 R7
(Before) R7
(After)

6. What does it do? LA 7,5(0,9) or LA 7,5(,9) R8 00 00 20 00 R9 R9
(Before) R7 R7
(After)

7. What does it do? LA 7,5 or LA 7,5(0,0) R7 00 00 12 34 R7
(Before) R7 R7
(After)
This is an effective way to load a “small” number into a register.
Small means < Why?

8. An Assembly Listing
LA 8,4(0,3) LA 8,4(,3) LA 8,4(3) LA 8,4(0,0) LA 8,4

9. LA Example use: Assume: TABLE DC F ‘1’ Assume address 1000 DC F ‘2’
TABENTRY DS F
You execute:
LA R7,8
LA R8,TABLE
LA R9,0(R7,R8)
MCV TABENTRY,0(R9)
R9 After:

10. Programming Tips
It’s easy to make a simple mistake by coding L for LA or LA for L. Give it a moment’s extra thought when you code these. Do you want an address (LA)? Or do you want the contents at an address (L)?
LA is often used for loading multiple base registers:
BASR R12,R0
USING *,R12,R11
LA R11,2048
LA R11,2048(R11,R12)

11. Try it in VisibleZ
Try the following programs:
la.obj