Addressing modes

BippyM · 24 January 2005, 18:20

Could some nice chappy explain to me (in English) the following: Adressing Modes

I know what they are called

Inherant
Regiser
Immediate
Absolute
Address Register Indirect
Address Register Indirect with displacement
Address Register Indirect with postincrement
Address Register Indirect with predecrement
Address Register Indirect with index and displacement
Program counter relative with displacement
Program counter relative with index and displacement

I've got Paul Overaa's Mastering Amiga Assembler and I also have an abacus assembler book and both explain how addressing works, but I must be thick or something cuz I just cannot get it in my head and understand it!

So what I want to know is:

How do they work?
In what situation would one be better than another?
maybe examples would be good that I can question

Codetapper · 24 January 2005, 19:45

They're just names and you don't have to know what they mean. It is just the difference between things like this:

moveq #5,d0
move.l d0,(a0)
move.l d0,(a0)+
move.l d0,-(a0)
move.l (5,a1),(a0)
move.l (5,a1),(a0)+
move.l (5,a1),-(a0)

etc...

BippyM · 24 January 2005, 19:59

Right /scratches head!!!

Joe Maroni · 25 January 2005, 08:14

if you get grips of this some day you will see it´s easier than you think...

jmmijo · 25 January 2005, 08:26

Quote:

Originally Posted by Codetapper

They're just names and you don't have to know what they mean. It is just the difference between things like this:

moveq #5,d0
move.l d0,(a0)
move.l d0,(a0)+
move.l d0,-(a0)
move.l (5,a1),(a0)
move.l (5,a1),(a0)+
move.l (5,a1),-(a0)

etc...

Man, I knew enough to be dangerous but that's about it, however let's see if the little gray cells know what some of this means here Codetapper

For instance:

move.l d0,(a0)

Means move.something from data zero to address zero ?!? Or was it the other way around, from address zero to data zero ?!?

Geeze, I guess I'm not remembering much myself

Joe Maroni · 25 January 2005, 10:36

ok, first:

moveq #5,D0 ;move the value 5 (decimal) to the dataregister 0
move.l d0,(a0) ;move the value that is located in d0 to the adress that stands in a0 (not in a0 direct, only to the adress that stands in a0...)

move.l d0,(a0)+ ;move the value that stands in d0 to the adress that stands in a0 and then increase the adress

move.l d0,-(a0) ;decrease first a0 and then move the value that stands in d0 to the adress that stands in a0

second will follow...

BippyM · 25 January 2005, 15:40

Quote:

Originally Posted by x_to

ok, first:

moveq #5,D0 ;move the value 5 (decimal) to the dataregister 0
move.l d0,(a0) ;move the value that is located in d0 to the adress that stands in a0 (not in a0 direct, only to the adress that stands in a0...)

move.l d0,(a0)+ ;move the value that stands in d0 to the adress that stands in a0 and then increase the adress

move.l d0,-(a0) ;decrease first a0 and then move the value that stands in d0 to the adress that stands in a0

second will follow...

Lets see if I follow that...

moveq #5,d0 ;puts 5 into d0 (like youi said

)
move.l d0,(a0) ; so d0=5 and a0 points to $5443, so a0 now points to $5448 or is the actual contents of the address changed?
move.l d0,(a0)+ ; so a0 would become $5449 (add 5 to a0 then +1) or would the address directly be changed as above and then a0 points to the next address?
move.l d0,-(a0) ; as above but reversed??

IFW · 25 January 2005, 15:53

Very simple:
#: means a direct value
() means a location defined by the value in the parentheses
If there is an additional offset by a direct value it is outside or inside the parentheses depending on old or new style mnemonic syntax. Regardless the result is the sum of the values listed.

moveq #5,d0: move direct value 5 to register d0
Don't bother with the q thing, it is a cpu optimization that any decent assembler program will automatically add to it.

move.l d0,(a0): move the value of register d0 to the location stored in a0

move.l d0,(a0)+: same as above then increment a0 by the size of the operand in this case 4, as it is a longword

etc

You really should read some decent books on cpu architectures first.
A simple 8 bit cpu is a good start, to understand how and why 16 bit cpus are different.
Also 68k were designed to work nicely with compiled C code, many of the addressing modes are similar to typical C mechanisms so knowing C can help a lot.

BippyM · 25 January 2005, 16:01

I have a few books on Amiga asm and I think I have a book on the 68k cpu itself!!

Maybe I should start reading them and playing around with some source eh!

IFW · 25 January 2005, 16:11

First experiment with your own source code, reading others' on an amiga is not very useful as long as you have trouble with the basics, as there are plenty of things normally going on in a native miggy program, most related to programming the custom chips.
Write very simple programs of just a few lines if you have trouble understanding the addressing modes, then watch them execute step by step in a debugger, showing memory locations, values and registers.
Devpac 3 is excellent for this.

BippyM · 25 January 2005, 16:13

Cool and I just happen to have a perfect boxed copy of devpac3 with full manuals and the works

Joe Maroni · 25 January 2005, 19:26

i use the asmpro...also very nice...

Codetapper · 25 January 2005, 20:44

Quote:

Originally Posted by IFW

moveq #5,d0: move direct value 5 to register d0
Don't bother with the q thing, it is a cpu optimization that any decent assembler program will automatically add to it.

However, it's only 5 letters to type moveq and 6 to type move.l so it's worth manually typing them just to save your fingers!

This of course assumes that you know the value you are moving is within 8 bit range. As IFW says, if the value is a constant or might change at some point, move.l is better.

And I also think the Asm-One debugger is awesome - I've never been able to work out the Devpac/MonAm debugger (to be honest, I don't have a manual for it but the Asm-Pro debugger is so logical it doesn't need a manual).

25 January 2005, 23:20

Bippy,

This might help to get to grips with the basics of the 68000:

http://www.hildreds.freeserve.co.uk/WISM68/

But that's not the hard part (learning the instructions). The hard part is learning how to program all the Amiga's custom tricks and a million other things

BippyM · 25 January 2005, 23:31

cheers Jim I'll give it a butchers

jmmijo · 25 January 2005, 23:35

Quote:

Originally Posted by bippym

cheers Jim I'll give it a butchers

Ah the trials and trivails of Supervisor mode

AmiGer · 26 January 2005, 07:57

The 68000 Programmer's reference manual can be downloaded from

http://www.freescale.com/webapp/sps/...018rH3YTLC4622

or at

http://www.technoplaza.net/downloads....php?program=9

Just 646 pages, have fun...

redblade · 03 February 2005, 09:57

hmm on aminet one of the asm tutorials by c00l-g, has 3 files about amiga assembler and amiga hardware in it, and in one of those files, the addressing modes are mentioned and examples given.

either asm_course.lha or asmcourse.lha

24 January 2005, 18:20	#1
BippyM Global Moderator Join Date: Nov 2001 Location: Derby, UK Age: 48 Posts: 9,355	Addressing modes Could some nice chappy explain to me (in English) the following: Adressing Modes I know what they are called Inherant Regiser Immediate Absolute Address Register Indirect Address Register Indirect with displacement Address Register Indirect with postincrement Address Register Indirect with predecrement Address Register Indirect with index and displacement Program counter relative with displacement Program counter relative with index and displacement I've got Paul Overaa's Mastering Amiga Assembler and I also have an abacus assembler book and both explain how addressing works, but I must be thick or something cuz I just cannot get it in my head and understand it! So what I want to know is: How do they work? In what situation would one be better than another? maybe examples would be good that I can question

24 January 2005, 19:45	#2
Codetapper 2 contact me: email only! Join Date: May 2001 Location: Auckland / New Zealand Posts: 3,182	They're just names and you don't have to know what they mean. It is just the difference between things like this: moveq #5,d0 move.l d0,(a0) move.l d0,(a0)+ move.l d0,-(a0) move.l (5,a1),(a0) move.l (5,a1),(a0)+ move.l (5,a1),-(a0) etc... Last edited by Codetapper; 24 January 2005 at 20:53.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
question on resourcing relative addressing	ara	Coders. Asm / Hardware	5	04 February 2012 23:42
Non-interlaced screen modes	8bitbubsy	support.Other	0	06 December 2010 02:01
Memory addressing	CmdrVimes	Coders. General	7	25 October 2010 22:20
Memory Addressing Architecture	Zetr0	support.Hardware	2	10 July 2007 16:55
Screen modes	AndySch	support.Apps	3	02 July 2006 07:01

24 January 2005, 19:59	#3
BippyM Global Moderator Join Date: Nov 2001 Location: Derby, UK Age: 48 Posts: 9,355	Right /scratches head!!!

25 January 2005, 08:14	#4
Joe Maroni Moderator Join Date: Feb 2003 Location: Germany Age: 44 Posts: 1,303	if you get grips of this some day you will see it´s easier than you think...

25 January 2005, 10:36	#6
Joe Maroni Moderator Join Date: Feb 2003 Location: Germany Age: 44 Posts: 1,303	ok, first: moveq #5,D0 ;move the value 5 (decimal) to the dataregister 0 move.l d0,(a0) ;move the value that is located in d0 to the adress that stands in a0 (not in a0 direct, only to the adress that stands in a0...) move.l d0,(a0)+ ;move the value that stands in d0 to the adress that stands in a0 and then increase the adress move.l d0,-(a0) ;decrease first a0 and then move the value that stands in d0 to the adress that stands in a0 second will follow...

25 January 2005, 15:53	#8
IFW Moderator Join Date: Jan 2003 Location: ... Age: 52 Posts: 1,838	Very simple: #: means a direct value () means a location defined by the value in the parentheses If there is an additional offset by a direct value it is outside or inside the parentheses depending on old or new style mnemonic syntax. Regardless the result is the sum of the values listed. moveq #5,d0: move direct value 5 to register d0 Don't bother with the q thing, it is a cpu optimization that any decent assembler program will automatically add to it. move.l d0,(a0): move the value of register d0 to the location stored in a0 move.l d0,(a0)+: same as above then increment a0 by the size of the operand in this case 4, as it is a longword etc You really should read some decent books on cpu architectures first. A simple 8 bit cpu is a good start, to understand how and why 16 bit cpus are different. Also 68k were designed to work nicely with compiled C code, many of the addressing modes are similar to typical C mechanisms so knowing C can help a lot.

25 January 2005, 16:01	#9
BippyM Global Moderator Join Date: Nov 2001 Location: Derby, UK Age: 48 Posts: 9,355	I have a few books on Amiga asm and I think I have a book on the 68k cpu itself!! Maybe I should start reading them and playing around with some source eh!

25 January 2005, 16:11	#10
IFW Moderator Join Date: Jan 2003 Location: ... Age: 52 Posts: 1,838	First experiment with your own source code, reading others' on an amiga is not very useful as long as you have trouble with the basics, as there are plenty of things normally going on in a native miggy program, most related to programming the custom chips. Write very simple programs of just a few lines if you have trouble understanding the addressing modes, then watch them execute step by step in a debugger, showing memory locations, values and registers. Devpac 3 is excellent for this.

25 January 2005, 16:13	#11
BippyM Global Moderator Join Date: Nov 2001 Location: Derby, UK Age: 48 Posts: 9,355	Cool and I just happen to have a perfect boxed copy of devpac3 with full manuals and the works

25 January 2005, 19:26	#12
Joe Maroni Moderator Join Date: Feb 2003 Location: Germany Age: 44 Posts: 1,303	i use the asmpro...also very nice...

25 January 2005, 23:20	#14
Jim Posts: n/a	Bippy, This might help to get to grips with the basics of the 68000: http://www.hildreds.freeserve.co.uk/WISM68/ But that's not the hard part (learning the instructions). The hard part is learning how to program all the Amiga's custom tricks and a million other things

25 January 2005, 23:31	#15
BippyM Global Moderator Join Date: Nov 2001 Location: Derby, UK Age: 48 Posts: 9,355	cheers Jim I'll give it a butchers

26 January 2005, 07:57	#17
AmiGer Registered User Join Date: Sep 2002 Location: Germany Posts: 349	The 68000 Programmer's reference manual can be downloaded from http://www.freescale.com/webapp/sps/...018rH3YTLC4622 or at http://www.technoplaza.net/downloads....php?program=9 Just 646 pages, have fun...

03 February 2005, 09:57	#18
redblade Zone Friend Join Date: Mar 2004 Location: Middle Earth Age: 40 Posts: 2,127	hmm on aminet one of the asm tutorials by c00l-g, has 3 files about amiga assembler and amiga hardware in it, and in one of those files, the addressing modes are mentioned and examples given. either asm_course.lha or asmcourse.lha

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)