1. ECE 445 CS1251 Computer Organization Carl Hamacher
Addressing Modes
CS1251
Computer Organization
Carl Hamacher
11/7/2018
Department of Information Technology
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2. Department of Information Technology
ECE 445
Addressing Modes
Name
Syntax
Addressing Function
Immediate
#Value
Operand = Value
Register Ri
EA = Ri
Absolute (Direct)
LOC
EA = LOC
Indirect
(Ri)
(LOC)
EA = [Ri]
EA = [LOC]
Index
X(Ri)
EA = [Ri] + X
Relative
X(PC)
EA = [PC] + X
Autoincrement
(Ri)+
EA = [Ri]; Ri  [Ri] + 1
Autodecrement
–(Ri)
Ri  [Ri] – 1; EA = [Ri]
EA = Effective Address
11/7/2018
Department of Information Technology
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3. Absolute, Register, Immediate
ECE 445
Absolute, Register, Immediate
Assembly Language
MOVE NUM1,R1
MOVE #1,R2
ADD #1,R1
ADD R1,R2
Register Transfer Notation
R1  [NUM1]
R2  1
R1  1 + [R1]
R2  [R1] + [R2]
11/7/2018
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4. Department of Information Technology
ECE 445
Instruction Results
MOVE #NUM2,R0
MOVE NUM1,R1
MOVE #5,R2
ADD #-1,R2
MEM
REGS
Label
Addr
Contents 0B
NUM1 0C
X"000A"
NUM2 0D
X"0007" 0E
Addr
Contents 1 2 3
X"000D"
X"000A"
X"0005"
X"0004"
11/7/2018
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5. Department of Information Technology
ECE 445
Indirect Addressing
Assembly Language
MOVE (R0),R2
MOVE (R1),NUM1
ADD (R3),R1
ADD #1,(R3)
Register Transfer Notation
R2  [MEM([R0])]
MEM(NUM1)  [MEM([R1])]
R1  [MEM([R3])] + [R1]
MEM([R3])  1 + [MEM([R3])]
11/7/2018
Department of Information Technology
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6. Department of Information Technology
ECE 445
Instruction Results
MOVE (R0),R2
MOVE (R1),NUM1
ADD #1,(R3)
MEM
REGS
Label
Addr
Contents 12
NUM1 13
NUM2 14
X"0007" 15
X"0009"
Addr
Contents 1 2 3
X"0012"
X"0003"
X"0004"
X"0014"
X"0009"
X"0015"
X"0007"
11/7/2018
Department of Information Technology
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7. Loop to Add n Numbers MOVE N,R1 Counter CLEAR R0 Accumulator LOOP
ECE 445
Loop to Add n Numbers
MOVE N,R1
Counter
CLEAR R0
Accumulator
LOOP
Determine address of "Next" number and add "Next" number to R0
Program loop
DECREMENT R1
BRANCH>0 LOOP
PC  [PC] + Offset (CC>0)
MOVE R0,SUM
. . .
SUM N n
NUM1
. . .
NUMn
11/7/2018
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8. Use of Indirect Addressing
ECE 445
Use of Indirect Addressing
MOVE N,R1
MOVE #NUM1,R2
CLEAR R0
LOOP ADD (R2),R0
ADD #1,R2
DECREMENT R1
BRANCH>0 LOOP
MOVE R0,SUM R0
Accumulator R1 n
Counter R2
NUM1
Pointer R3
SUM N n
NUM1
. . .
NUMn
11/7/2018
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9. Indexed Addressing (Arrays)
ECE 445
Indexed Addressing (Arrays)
Assembly Language
MOVE X(R0),R1
MOVE R2,Y(R3)
ADD Z(R1),R2
Register Transfer Notation
R1  [MEM(X + [R0])]
MEM(Y + [R3])  [R2]
R2  [MEM(Z + [R1])] + [R2]
11/7/2018
Department of Information Technology
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10. Assembly Language to Machine Instructions
ECE 445
Assembly Language to Machine Instructions
Assembler (Program)
Source Program (Assembly Language)
Object Program (Machine Instructions)
Assembler Directives (Commands)
How to Interpret Names
Where to Place Instructions in Memory
Where to Place Data in Memory
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11. Department of Information Technology
ECE 445
Assembler Directives
START
100
MOVE N,R1
SUM EQU
ORIGIN 201
N DATAWORD 300
NUM1 RESERVE 300
ORIGIN 100
START MOVE N,R1
MOVE #NUM1,R2
CLR R0
LOOP ADD (R2),R0
ADD #1,R2
DEC R1
BGTZ LOOP
MOVE R0,SUM
RETURN
END START
101
MOVE #NUM1,R2
102
CLEAR R0
LOOP
103
ADD (R2),R0
104
ADD #1,R2
105
DECREMENT R1
106
BRANCH>0 LOOP
107
MOVE R0,SUM
. . .
SUM
200 N
201
300
NUM1
202
11/7/2018
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12. Department of Information Technology
ECE 445
Two-Pass Assembler
First Pass
Create Symbol Table
Names Assigned Numerical Values
Second Pass
Translates Assembly Language to Machine Code
Substitutes Values for Names
Computes Branch Offsets
11/7/2018
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13. Encoding of Machine Instructions
ECE 445
Encoding of Machine Instructions
Opcode
Source
Dest
Other Info
One-Word Instruction
Opcode
Source
Dest
Other Info
Two-Word Instruction
Memory Address / Immediate Operand
Opcode Ri
Other Info
Three-Operand Instruction Rj Rk
11/7/2018
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14. HW2 Instruction Encoding
ECE 445
HW2 Instruction Encoding OP
SRC
DST
VALUE IR
Assembly Language
OP SRC, DST
Example
MOVE R1,R2
Register Transfer Notation
DST  [SRC] OP [DST]
Example
R2  [R1]
11/7/2018
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15. Department of Information Technology
ECE 445
HW2 Addressing Modes
Mode
REG #
Name
Syntax
Addr Fn
SRC 00
00-11
Register Direct Rn
EA = Rn 01
Register Indirect
(Rn)
EA = [Rn] 10 XX
Immediate
#Value
Operand = Value 11
Absolute
Value
EA = Value
Mode
REG #
Name
Syntax
Addr Fn
DST
00-11
Register Direct Rn
EA = Rn 1 XX
Absolute
Value
EA = Value
EA = Effective Address
11/7/2018
Department of Information Technology
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16. Single-Bus Architecture
ECE 445
Single-Bus Architecture
BUS A 6 6
MAR 3 PC
ROM
MEM 1
MDR 2 IR 1 1 2 6
MUX
MUX 2 Y 1 1
REGS A B
ALU R Z
11/7/2018
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17. SRC Control Flowchart Reg Direct 00 Reg Indir 01 Y  [REGS([SRC_REG])]
ECE 445
SRC Control Flowchart
Reg Direct 00
Reg Indir 01 N N Y Y
Y  [REGS([SRC_REG])]
MAR  [REGS([SRC_REG])]
MDR  [MEM([MAR])]
Y  [MDR]
11/7/2018
Department of Information Technology
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18. Department of Information Technology
ECE 445
SRC Control Flowchart
Immediate 10
Absolute 11 N N Y Y
Y  Value
MAR  Value
MDR  [MEM([MAR])]
Y  [MDR]
11/7/2018
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19. Department of Information Technology
ECE 445
DST Control Flowchart
Reg Direct
Absolute 1 N N Y Y
REGS([DST_REG])  [Z]
MAR  Value
MDR  [Z]
MEM([MAR])  [MDR]
11/7/2018
Department of Information Technology
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20. Department of Information Technology
ECE 445
Questions?
11/7/2018
Department of Information Technology
RJH