MCO556

- 1 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 1

MCO556

Assembly Language

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MCO556

- 2 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 2

2

Programming Model

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MCO556

- 3 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 3

3

HCS12 Instructions

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MCO556

- 4 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 4

4

Addressing Modes

• Inherent - no operands

• Immediate - operand is in the program

• Direct - operand in first 256 bytes

• Extended - operand anywhere in memory

• Relative - branch instructions only

• Index - sum of index register and offset

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MCO556

- 5 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 5

5

Index Addressing

• 5 bit Constant offset

• 9 bit Constant offset

• 16 bit Constant offset

• 16 bit Constant Indirect

• Auto Post/Pre De/Increment

• Accumulator Offset

• Accumulator D Indirect

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MCO556

- 6 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 6

6

5 bit Constant Offset Indexed

Base index register X, Y, SP or PC.

Range of the offset -16 to +15.

Example:

Load Acc A with contents held at address X + 0

ldaa 0,X

Store contents of Acc B to address held in Y - 10

stab -8,Y

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MCO556

- 7 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 7

7

9 bit Constant Offset Indexed

Base index register X, Y, SP or PC.

Range of the offset -256 to +255.

Example:

Load Acc A with contents held at address X + 255

ldaa $FF,X

Store contents of Acc B to address held in Y - 20

ldab -20,Y

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MCO556

- 8 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 8

8

16 bit Constant Offset Indexed

Base index register X, Y, SP or PC.

Access to any location in 64Kbyte range.

Example:

Load Acc A with contents held at address X + 2000

ldaa 2000,X

Store contents of Acc B to address held in Y + 4000

staa 4000,Y

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MCO556

- 9 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 9

9

Auto Pre/Post De/Increment Indexed

Base index register X, Y, or SP.Index register incremented or decrementedIndexing before or after index register is changedIndex change -8 to -1 or +1 to +8

Example:Decrement SP by 1 and save Acc A at addressstaa 1,-SP

Load Reg X with contents held at SP and advance SP by 2 locations ldx 2,SP+

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MCO556

- 10 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 10

10

Accumulator Offset Indexed

Address sum of accumulator and base index

Base index register X, Y, SP or PC.

Accumulator A, B, D(16 bit)

Example:

Load Acc A with contents held at address X + B

ldaa B,X

Store contents of Acc B to address held in Y + B

stab B,Y

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MCO556

- 11 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 11

11

16 bit Constant Indirect Indexed

Base index register X, Y, SP or PC.

Index plus offset is address of memory which is the effective address

Store contents of Acc A to address (2345 – 4) held in Y

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MCO556

- 12 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 12

12

Accumulator D Indirect Indexed

Base index register X, Y, SP or PC.

Index plus Acc D is address of memory which is the effective address

Store contents of Reg X to address (2345 + 4) sum of D and Y

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MCO556

- 13 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 13

13

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MCO556

- 14 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 14

14

Fields of a HCS12 InstructionLabel

• starts with letter and followed by letters, digits, or special symbols (_ or .)

• start from any column if ended with “:”

• start from column 1 if not ended with “:”

Opcode

• contains the mnemonic of a machine instruction or an assembler directive

• is separated from the label by at least one space

Operand

• follows opcode and is separated from opcode by at least one space

• operands for instructions or arguments for assembler directives

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MCO556

- 15 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 15

15

Instruction Fields

loop ADDA #$40 ; add 40 to accumulator A

(1) “loop” is a label

(2) “ADDA” is an instruction mnemonic

(3) “#$40” is the operand

(4) “add 40 to accumulator A” is a comment

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MCO556

- 16 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 16

16

Assembly Directives

• define data and symbol

• reserve and initialize memory locations

• set assembler and linking condition

• specify output format

• Specifies the end of a program.

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MCO556

- 17 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 17

17

Assembler Directives

END - ends a program

ORG - sets new value for location counter

ORG $1000

LDAB #$FF

db (define byte)

dc.b (define constant byte)

fcb (form constant byte)

org $800

array db $11,$22,$33,$44

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MCO556

- 18 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 18

18

Assembler Directivesdw (define word)

dc.w (define constant word)

fdb (form double bytes)

vec_tab dw $1234, $5678

fcc (form constant character)

msg fcc “Please enter 1, 2 or 3:”

ds.w (define storage word)

rmw (reserve memory word)

dbuf ds.w 20

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MCO556

- 19 – Seneca College – School of Information and Communications Technology G VandeBelt 113

Slide 19

19

Assembler Directives

equ (equate)

loop1_cnt equ 100

loop2_cnt equ 50

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