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CPE215 Lecture 31
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Opcode Mnemonic. Operand(s) Comment. Label and Comment are optional. MC68000 Syntax ... XREF permits access to external subroutines, such as those for keyboard input, ... – PowerPoint PPT presentation
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Title: CPE215 Lecture 31
1
CPE-215 Lecture 31
- Motorola Code
2
Line Fields
- Each line in MC68000 is divided into four fields
- Label
- Opcode Mnemonic
- Operand(s)
- Comment
- Label and Comment are optional.
3
MC68000 Syntax
- Directives
- XREF directive
- Assembly Language Instructions
- Data Section
- DATA directive
- Define Constant directives
- Define Storage directives
- End Directive
4
XREF Directives
- XREF permits access to external subroutines, such
as those for keyboard input, line termination,
and display output. - Every assembler has a number of these, and they
are linked in when the program is assembled.
5
Input/Output Routines
- Each assembler has routines to get inputs from
the keyboard and display outputs on the screen. - These are linked into the program in response to
the XREF directive. - DECIN, DECIN__LONG
- DECOUT, DECOUT__LONG
- HEXIN, HEXIN__LONG
- HEXOUT, HEXOUT__LONG
- NEWLINE
- STRIN
- STROUT
6
STRIN
- You need a buffer
- bufname DS.B 80
- The buffer address is loaded into A0
- LEA bufname,A0
- The buffer size is loaded into D0
- MOVE.W 80,D0
- Then you jump to the subroutine
- JSR strin
7
Where Stuff Goes
- Input subroutines store the input from the
keyboard in register D0. - Output subroutines store whatever is in D0 to the
display. - In the case of strings, A0 holds the address of
the string or buffer, and D0 holds the length of
the string or size of the buffer.
8
STROUT
- You need a string
- msg DC.B This string has 29 characters
- The string address is loaded into A0
- LEA msg,A0
- The string size is loaded into D0
- MOVE.W 29,D0
- Then you jump to the subroutine
- JSR strout
9
DATA Directive
- This directive is used to define the beginning of
the data section.
10
Data Directives
- Define Constant
- DC.ltsizegt ltconstantsgt
- Can be Byte, Word, Long word
- Define Storage
- DS.ltsizegt ltcountgt
- Can be Byte, Word, Long word
- Not initialized
- Define Constant Block
- DCB.ltsizegt ltcountgt,ltvaluegt
- Can be Byte, Word, Long word
- All of these can be used to create arrays
11
Sample Program 1 -- Pascal
- program example (output)
- var
- i, j, k integer
- begin
- i 75
- j 4
- k i j 6
- writeln (k)
- end.
12
Sample Program 1 -- C
- include ltstdio.hgt
- void main (void)
- int i 75
- int j 4
- int k
- k i j 6
- printf (d\n, k)
13
MC68000 Code, Sample 1
- xref decout, newline, stop
- program instruction section
- start move.w I,d0
- add.w j,d0
- subi.w 6,d0
- move.w d0,k
- jsr decout
- jsr newline
- jsr stop
- data declaration section
- data
- i dc.w 75
- j dc.w 4
- k ds.w 1
- end
14
MC68000 Code, Sample 2
- This program computes 2n, where n is input.
- Number must be in the range of 0 to 14.
- The table entry for n is printed out.
- NOTE This sample does not include any prompts
for input, so the code could be improved vastly
for user-friendliness.
15
Code for Sample 2
- xref decout, decin, newline, stop
- start lea p2table,a0
- jsr decin
- bmi out
- cmpi.w 14,d0
- bgt out
- asl.w 1,d0
- move.w (0,a0,d0.w),d0
- jsr decout
- jsr newline
- out jsr stop
- data
- p2table dc.w 1,2,4,8,16,32,64,128,256,512,1024
- dc.w 2048,4096,8192,16384
- end
16
Sample 3, Subroutine
- This program computes Y X2 X using a
subroutine. - Since D1 is used as a scratch register by the
subroutine, it must be pushed and popped within
the subroutine.
17
Sample 3, Main Program
- XREF DECOUT,NEWLINE,STOP
- START MOVEQ 6,D1 Loop 7 times
- MOVEQ 1,D2
- LOOP MOVE.W D2,D0
- JSR COMPUTE
- JSR DECOUT
- JSR NEWLINE
- ADDQ.W 1,D2
- DBRA D1,LOOP
- JSR STOP
- COMPUTE
- END
18
Sample 3, Subroutine
- COMPUTE MOVE.L D1,-(SP)
- Push D1 on the stack
- MOVE.W D0,D1
- MULU D0,D1
- ADD.W D1,D0
- MOVE.L (SP),D1 Pop D1
- RTS
19
Saving More Stuff
- Save
- MOVE.L A0,-(SP)
- MOVE.L D2,-(SP)
- MOVE.L D1,-(SP) MOVEA.L ?
- or
- MOVEM.L D1-D2/A0,-(SP)
- Restore
- MOVE.L (SP),D1
- MOVE.L (SP),D2
- MOVEA.L (SP),A0
- or
- MOVEM.L (SP),D1-D2/A0
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