[Coco] questions about constants

[Wayne Campbell]

OK. I'm consolidating my reply to both Art and Lothan.

I understand about them being pseudo op codes. I understand that the actual labels are:

fcb = form one byte
fdb = form double byte
fcc = form character string
fcs = form character string with hi-bit set on last byte

In respect to the data being put after the last rts instruction, that makes sense. In Basic09, I put my DATA statements after the last RETURN statement. In the I-Code, the DSAT and VDT occur after the last instruction statement. So, when I de-compile with disasm, all the rmb's and fcb's at the top are actually data contained at the bottom of the module. Is that correct?

I know that source files can be divided into parts, like .h for a header file, .a for the assembly source, .r for a linker file. Is there a particular order a header file is parsed in? I know that org sets the numerical origin of the rmb's that follow, but sometimes I see the org value change. In addition, the rmb's and fcb's at the beginning of the disasm output don't correspond directly to the header file. Does that mean the assembler parsed different parts in a different order?

Wayne




________________________________
From: Arthur Flexser <flexser at fiu.edu>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Saturday, September 12, 2009 6:37:54 PM
Subject: Re: [Coco] questions about constants

These are not opcodes, which may explain why you had trouble finding
them--they wouldn't appear in a table of opcodes.  They are
"pseudo-ops"--assembler commands that don't themselves assemble into any
bytes, but instead tell the assembler to do something.  So, if you simply
want the byte $20, say, to be included in the assembler output at some
location you've given the label "HERE" to, you'd put

HERE      FCB  $20

Or, to do this with the double byte $1234, you'd use

HERE     FDB   $1234

I've don't recollect hearing of FCS--it may be a pseudo-op that only some
assemblers recognize.   FCC is the thing that is generally used for strings:

HERE    FCC /Put this string here./

Probably some assemblers only allow a single data character after FCC and
demand that FCS be used when multiple characters are desired.

Generally, you'd these someplace that does not contain executable
instructions, like after an RTS, to include data values that you want your
program to have access to.

Art


________________________________
From: Lothan <lothan at newsguy.com>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Saturday, September 12, 2009 6:44:17 PM
Subject: Re: [Coco] questions about constants

Actually, not quite. With OS-9 assemblers

fcs /Basic09/
-or-
fcs "Basic09"

is equivalent to:

fcc 'B'
fcc 'a'
fcc 's'
fcc 'i'
fcc 'c'
fcc '0'
fcb '9' + 0x80

or equivalently

fcc "Basic0"
fcb '9' + 0x80

The differentiation is the fcb is for a single byte, fcc is for character 
data, and fcs is for strings in which the last character has the high-bit 
set. There is no fci, fcr, fcd with the assemblers that came with OS-9 or 
the Development System.

The delimiters don't really matter quite so much with fcc/fcs so you can use 
/, ', ", and perhaps a few others depending on your needs, but the delimiter 
at the start of the string must be the delimiter used to end the string.

--------------------------------------------------
From: "Wayne Campbell" <asa.rand at yahoo.com>
Sent: Saturday, September 12, 2009 7:41 PM
To: <coco at maltedmedia.com>
Subject: [Coco] questions about constants

> 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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