[Coco] Assembly timing question

[Darren A]

On Mon, Mar 21, 2016 at 7:53 PM, Lee Patterson wrote:

> Looking at 6809 Assembly Language Programming by Leventhal, and trying to
> figure out cycle counts. Addressing modes
>
> 1) What addressing mode is LDA ,X+ using? I think it's extended direct
> addressing, which is 5 cycles.
> 2) leay 1,y is listed as 4+ cycles. How do I know how many the "+" is?
>
>

Both of those instructions use Indexed addressing.  There are several
variations of Indexed addressing.  LDA ,X+ is the 'post-increment by 1'
variation, while LEAY 1,Y would assemble as the '5-bit offset,
non-indirect' variation.

The "+" appears in the cycle count column because you need to add the
number of cycles associated with the particular Indexed variation to get
the total cycle count.  There should be a separate Indexed Addressing Mode
Table which lists the additional cycle counts (and byte counts) for each
variation.


- Darren