[Coco] questions about constants

[Lothan]

The ORG statement effectively sets the module offset to the address 
specified, although it can be a bit more complicated that than when defining 
structures. In effect, the code you give

 ORG 0
A.LABEL1 rmb 1
A.LABEL2 rmb 1
A.LABEL3 rmb 2
A.LABEL4 rmb 1
A.LABEL equ .

set the base to zero, then reserves one byte of memory for A.LABEL2, one 
byte for A.LABEL2, and so forth. Looking at the actual binary data, it would 
something like this:

00 00 00 00 00 ... remainder of binary data

An equate (or EQU) assigns a constant value to a label, but the label is 
actually replaced with the real value. In other words, take this code:

Zero EQU 0

MySub LDA Zero
 LDB 0
 RTS

Run that through the assembler, then disassamble the resulting binary and 
you'll see this:

MySub LDA 0
 LDB 0
 RTS

Going back to the top, A.LABEL EQU . is (if my brain is working half right) 
5 since the current module offset is 5.


--------------------------------------------------
From: "Wayne Campbell" <asa.rand at yahoo.com>
Sent: Sunday, September 13, 2009 4:14 PM
To: <coco at maltedmedia.com>
Subject: Re: [Coco] questions about constants

> I believe I understand the compiler directives and pseudo op codes better 
> now. In order to make sure I am looking at things correctly, the following 
> is true?
>
> org 0 sets the current . value to 0
>
> A.LABEL1 rmb 1 this A memory address is relative 0 to org
> A.LABEL2 rmb 1 this A memory address is relative 1 to org
>
> A.LABEL3 rmb 2 this A memory address is relative 2 or org
> A.LABEL4 rmb 1 this A memory address is relative 4 to org
>
> I know that equ is a system equate. What I'm not sure of, is what it is 
> equating.
>
> For example, say the above is true, and the following line comes next in 
> the list:
>
> A.LABEL5 equ
>
> does this mean that A.LABEL5 is being set to a value of 5, or the address 
> of 5 relative to org?
>
> Wayne
>
>
>
> ________________________________
> From: "jdaggett at gate.net" <jdaggett at gate.net>
> To: Wayne Campbell <asa.rand at yahoo.com>; CoCoList for Color Computer 
> Enthusiasts <coco at maltedmedia.com>
> Sent: Saturday, September 12, 2009 8:16:24 PM
> Subject: Re: [Coco] questions about constants
>
>
>
> Wayne
>
> FCB, FCC, FCS are assembler directives and not opcodes. What they do is 
> tell the
> assembler at that place in memory to reserve a single byte, a double byte 
> or multiple
> bytes. This used to hold a spot for data, screen prompts or table entries.
>
> Memory for all processors are in binary form. Integers are represented as 
> a binary
> number. They can be 8 bit, 16 bit or even 32 bit form. The more bits used 
> for integer the
> larger teh integer value you can have. 8 bit integers are limited 0 tp 255 
> if unsigned and -
> 127 to 128 if signed.
>
> Real numbers are stored as floating point binary numbers per the IEEE 
> standard. Well
> the Coco is not IEEE standard as the DEC Basic was written before the IEEE 
> standard
> was formed. To store a IEEE binary floating point number you need to 4 
> bytes for single
> precision, 8 bytes for double presicion. In single presicion you have a 23 
> bit mantissa,
> one sign bit and an 8 bit weighted exponent. For double presicion you have 
> an 11 bit
> weighted exponent, one sign bit and 62 bit mantissa.
>
> These require any program to reserve appropriate amount of memory for each 
> number
> used. You can use FCBs to reserve the bytes needed. In the case you only 
> want to
> declare the space and not assign a value,  you can use the asembler 
> directive RMB to
> reserve space. If you wish to reserve 4 bytes you can do this.
>
> FPACCA    RMB     4
>
> This will reseve 4 bytes for floating point accumaltor A.
>
> Assembler directives are a way to tell the assembler that all the code is 
> not machine
> code. Some maybe data, a macro so that you do not have to type the same 
> code over
> and over again.
>
> hope this helps
>
> james
>
> On 12 Sep 2009 at 16:41, Wayne Campbell wrote:
>
>> I have looked at a dozen tutorials on assembly language programming. None 
>> of them address the op codes fcb, fcc or fcs, so I'm asking the assembly 
>> gurus on this list to help explain this to me.
>>
>> What are the differences between fcb, fcc and fcs?
>> Is there a fci or fcr(/f/d) (for integer and real(/float/double) values)?
>>
>> I know that:
>>
>>   fcb = form constant byte   = any constant numeric byte value?
>>   fcc = form constant char   = any constant character that is 
>> displayable?
>>   fcs = form constant string = any constant string?
>>
>> Are the following equivalent, so far as the assembler is concerned?
>>
>> A. form constant byte:
>>
>>   fcb   $20
>>   fcb   $20
>>   fcb   $20
>>   fcb   $20
>>   fcb   $20
>>   fcb   $20
>>   fcb   $20
>>   fcb   $20
>>   fcb   $20
>>   fcb   $20
>>   fcb   $20
>>   fcb   $20
>>   fcb   $42 B
>>   fcb   $41 A
>>   fcb   $53 S
>>   fcb   $49 I
>>   fcb   $43 C
>>   fcb   $30 0
>>   fcb   $39 9
>>   fcb   $0A
>>
>> B. form constant string:
>>
>>   fcs   /            BASIC09/
>>   fcb   $0A
>>
>> C. would using form constant char be equivalent?
>>
>>   fcc   ' '
>>   fcc   ' '
>>   fcc   ' '
>>   fcc   ' '
>>   fcc   ' '
>>   fcc   ' '
>>   fcc   ' '
>>   fcc   ' '
>>   fcc   ' '
>>   fcc   ' '
>>   fcc   ' '
>>   fcc   ' '
>>   fcc   'B'
>>   fcc   'A'
>>   fcc   'S'
>>   fcc   'I'
>>   fcc   'C'
>>   fcc   '0'
>>   fcc   '9'
>>   fcb   $0A
>>
>> Wayne
>>
>>
>>
>>
>>
>> --
>> Coco mailing list
>> Coco at maltedmedia.com
>> http://five.pairlist.net/mailman/listinfo/coco
>
>
>
>
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