Re: Thanks...now a New problem...

[David.Empson@bbs.actrix.gen.nz]

In article <1me4kcINN9k9@master.cs.rose-hulman.edu> julichjh@NeXTwork.Rose-Hulman.Edu (Joseph H Julicher) writes:
>
> I am trying to read the A/D converter on the DOC....
> is the following code workable??????

I presume the 'c' characters in your asm function are actually '#'
characters?  (e.g. sep c0x20   should be sep #0x20)  I've corrected
them as such.  Pretty weird data corruption, if you ask me!

> 
> #include <stdio.h>
> asm int getAD(void)
> {
>     sep #0x20     /* Short accumulator */
> loop1:
>     lda >0xC03C   /* Get sound control (forced long addressing mode) */
>     bpl DOCready  /* loop until DOC is ready */
>     jmp loop1
> 
> DOCready:
>     and #0xBF     /* make sure I am reading DOC data */
>     sta >0xC03C   /* rewrite sound countrol */
>     lda #0xE1	  /* as auto increment is on.. second read will be the A/D */
>     sta >0xC03E   /* store $E1 in sound address pointer */
>                   /* should allow A/D register to be read on the second pass */
>     lda >0xC03D   /* read the audio data */
>     lda >0xC03D   /* reads lag by a read cycle so I read again */

[the above two lines came through as 'lda >0xC3D', so I've corrected them]

>     rep #0x20     /* Long accumulator */
>     rtl           /* Return with sample in A */
> }

The above code will not work as an in-line function, because the ORCA/C
inline assembler doesn't know about 8-bit immediate mode for the
accumulator and index registers.  Your 'and #0xBF' instruction will
actually generate a 16-bit operand, which will result in a BRK when the
code is executed.

The sep and rep instructions are handled correctly, but LDA, etc. aren't.

You have to perform all immediate-mode operations in 16 bits, turn
this into an external assembly language function (written with
ORCA/M), or use some other addressing mode to get the 8-bit constants.
For example, you could set up a local (direct page) variable with the
appropriate constants.

Other than that, the function should work fine, except that you will
end up with a random value in the high-order byte of the accumulator.
After doing the final REP #0x20, do an AND #0x00FF, to make sure the
high byte of the accumulator is zero.
-- 
David Empson

Internet: David.Empson@bbs.actrix.gen.nz    EMPSON_D@kosmos.wcc.govt.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand