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9/20/6 Lecture 2 - Prog Model 1

Architecture, Data

Types and Addressing Modes

9/20/6 Lecture 2 - Prog Model 2

Lecture Overview

 Assembler Language

 Programmers Model

 Registers

 Addressing Modes

9/20/6 Lecture 2 - Prog Model 4

Assembler Directives

 TTL

 “Title” – gives the program a user-defined name

 EQU

 **Links a pneumonic name to a value. Very valuable in making the program “readable”.  Example to reserve 128 bytes for a stack.  STACK_FRAME EQU 128 Define a stack frame of 128 bytes  ***  LINK A1,# -STACK_FRAME

9/20/6 Lecture 2 - Prog Model 5

Assembler Directives (2)

 DC

 Define constant. Allows the programmer to set memory locations to specific values.  Qualifier specifies data type: .B, .W, .L ORG $ FST DC.B 10, 66 Set constants of 10 and 66 DC.L $0A1234 Store $000A1234 in memory STR DC.B „April‟ Store ASCII values

9/20/6 Lecture 2 - Prog Model 7

Assembler Code Example

9/20/6 Lecture 2 - Prog Model 8

Programmers Model

 When looking at any architecture what does

the programmer see?

 REGISTERS (General purpose)  ADDRESS REGISTERS  SPECIAL PURPOSE REGISTERS  MEMORY  Allowable operations and data transfers supported

9/20/6 Lecture 2 - Prog Model 10

Address Registers

 8 Address Regs

 Labeled A0 to A

 Entire 32 bits is single entity value

 Any operation permitted on Ai is also allowed

on Aj

 2‟s complement value treatment

 Used in instructions to address memory

9/20/6 Lecture 2 - Prog Model 11

Special Purpose Registers

 2 such registers

 PC – Program Counter  Contains the address of the next instruction to be executed.  SR – Status Register  16 bits divided into two bytes  MSB – System byte – control operation mode  LSB – Condition codes

9/20/6 Lecture 2 - Prog Model 13

Addressing Modes

 Modes supported are reflective of even the most

modern architecture

 Some Notation

 [Dx] means the “contents of”  % num means binary  $ num means hexadecimal   indicates transfer of information

 Table on page 27 lists meaning of symbols and

notation

9/20/6 Lecture 2 - Prog Model 14

Immediate Addressing

 ACTION: The value of the operand (data) is loaded into the specified register at the time the program runs.  The value of the operand is used in the operation  Note that general form of instructions is  Operation #Source, Destination  MOVE.W #$8123,D3 [D3(0:15)]$  Fill the low order bytes of De  MOVE.L #$8123,D3 [D3(0:31)]$  Fills all 32 bits of register D

9/20/6 Lecture 2 - Prog Model 16

Register Direct Addressing

 Register to register operation

 The assembler instruction lists both register

which will be used for operand of the operation

to be performed

 The 2nd^ register listed is both the 2nd^ operand of

the operation and gets the results of the

operation.

 Example: MOVE.L D0,D

 Effect: [D3]  [D0]

9/20/6 Lecture 2 - Prog Model 17

Address Register Indirect

 Register Indirect means that the address of the operand is in a register, the address registers.  Ex: ASSEMBLERMOVE.L (A0), D3^ [D3]RTL  [M(A0)] MOVE.W D4, (A6) [M([A6])]  [D4(0:15)]

Forms of Address Reg. Indirect (2)

 Address Register Indirect with displacement

 A 16-bit displacement is specified in instruction  Displacement added to address register to obtain the effective address of the operand

 Register Indirect with Index Addressing

 Effective address is calculated by adding the address register + 8-bit signed displacement + contents of general purpose register  Ref fig 2.15 of text, pg.

9/20/6 Lecture 2 - Prog Model 19

9/20/6 Lecture 2 - Prog Model 20

PC Relative

 Similar to register indirect except that the

address of the operand is specified with

respect to the PC contents.

 Allows data to be located relative to the

location of the program in memory, i.e.,

relative to the Program Counter –

allows WHAT????

 Restricted to only the source operand