[Coco] Quick 6809 Q for night owls in the US

William Astle lost at l-w.ca
Tue Apr 15 10:14:08 EDT 2014


Actually, LD and ST both set flags based on the value being loaded or 
stored regardless of register involved. N and Z get set as expected and 
V gets cleared. C is not affected.

LEAS and LEAU do not affect any flags, of course. LEAX and LEAY affect 
only Z.

All this still adds up to the original point that you can't use U or S 
for the loop. (Well, you can, but you'd need a "CMPU #0" or "CMPS #0" 
before the BNE instruction. Which might be fine if you need a longer 
delay and are okay with using an extra code bytes.) You can, however, 
use X or Y for the loop counter.

On 14-04-15 07:37 AM, Steve wrote:
> Tim,
> Can't use the U (or S) register for this loop since the Z-flag is not
> set when doing LEA or LD operations.  These are stack registers and
> should not effect any flags since that would be bad for saving the state
> of the CPU.
> Steve
> On 4/15/2014 6:24 AM, tim at franklinlabs.com wrote:
>> I'm not at home to test but wouldn't this work??/
>>                  LDU    #1000
>> LOOP:    LEAU    -1,U
>>                  BNE    LOOP
>> All inside the CPU.
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