[Coco] Linville's ramblings on assembly vs machine code

[Mark McDougall]

On 11/07/2017 12:29 PM, Melanie and John Mark Mobley wrote:

> I got a surprise with I found that the following two instruction did not
> work the same:
>          CLRA     ; Clear A and the Carry Flag
>          LDA #$00 ; Clear A

Not sure this example has much to do with the ASM vs ML debate, but an 
interesting side note none-the-less.

When programming for different CPUs you come across similar subtleties 
with the Z flag; some clear it on a LOAD, some don't. Seemingly 
innocuous until you start porting code between processors. A good 
example is common practice on the Z80 with a comparison that then loads 
the accumulator with another value before a conditional branch...

> I think that it is important to note that the computer, for the most part,
> cannot distinguish between code and data.  Therefore you must jump in a
> valid address where the code is that you want to run.

It's related to the Halting Problem, which is why disassemblers simply 
can't get it right in every case.

Regards,

-- 
Mark McDougall
<http://retroports.blogspot.com.au>