1. Computer Science 210 Computer Organization
Machine Language Instructions:
Data Movement

2. Data Movement
Move data from memory to a register (load - LD, LDR, LDI, LEA)
Move data from a register to memory (store - ST, STR, STI)
Opcode Src or Address info
Dst

3. PC-Relative Mode To compute the memory address:
Sign-extend the address info (9-bit twos comp)
Add the result to the incremented PC
Opcode Src or Address info
Dst

4. PC-Relative: LD and ST RDst  M[PC + offset] M[PC + offset]  RSrc
RDst  M[PC + offset]
LD R x1AF
M[PC + offset]  RSrc
ST R x1AF
The operation is executed after the PC has been incremented
Address must be within +256 or -255 of the LD or ST instruction

5. Data Path for LD

6. Data Path for ST

7. PC-Indirect Mode To compute the memory address:
Sign-extend the address info (9-bit twos comp)
Add the result to the incremented PC
Use this address to locate another address in memory
Opcode Src or Address info
Dst

8. PC-Indirect: LDI and STI
RDst  M[M[PC + offset]]
LDI R x1CC
M[M[PC + offset]]  RSrc
STI R x1CC
Contents at the address is another address, which can be anywhere in memory

9. Data Path for LDI

10. Base + Offset Mode To compute the memory address:
Sign-extend the offset info (6-bit twos comp)
Add the result to contents of the base register
Opcode Src or Base Offset
Dst

11. Base + Offset: LDR and STR
RDst  M[base + offset]
LDR R R x1D
M[base + offset]  RSrc
STR R R x1D
Address does not depend on the PC
Offset must range from -32 to +31

12. Data Path for LDR

13. Load Effective Address (LEA)
Computes the address like PC-relative and just stores the result in the destination register
Memory is not accessed
Opcode Src or Address info
Dst

14. Data Path for LEA

15. For Friday
Control Instructions