[Coco] 6809 Test and Set instruction?

[jdaggett at gate.net]

Allen

There is no "SET" instruction for the MC6809. The "TST" (test) is a 
minimal information instruction. The "TST" should be performed on 
unsigned values. 

TST  yields TMP  <= M - 0 
 

Since no unsigned value is less than zero the "BLO" and "BLS"  
conditional branches have no use. It is better to use the conditional 
branch "BNE" after the "TST" instruction. The conditional branch 
"BHI" can be u sed after a "TST" though the "BNE is prefered. 

The a test the Z and N flags are affedted. The V,  overflow bit, is 
always cleared. No other CC register flags are affected. 

james


On 10 Jul 2006 at 23:08, Allen Huffman wrote:

> Does the 6809 have a test and set instruction?
> 
> 		-- Allen
> 
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