LZ-Adv: Help with zshell program and crashing

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LZ-Adv: Help with zshell program and crashing

In light of the discussion of plotting pixels and Jimmy Mardell's new 
tutorial on the same, I figured I would see what I could do.  I am new 
to asm programming, but I kind of like seeing how things work on my own 
(yes I am aware of FIND_PIXEL, but I want to make it work without, first 
so that I understand the inner workings of how the pixels are plotted). 
 Anyway, I quickly whipped together the following code and my pixel got 
plotted right where I expected it too.  Unfortunately, when I press a 
key, I get 2 1/2 rows of boxes and the TI 85 freezes up.  Can anyone 
point out what I am doing wrong?  For what it is worth, I have ROM v.10.




#include "TI-85.H"   	;this is the most current version - I think


.org 0			;Does this tell the calc where the prgm starts?	
		
.db "Graph a point",0	


        ld a,4
        out (5),a


        ROM_CALL(CLEARLCD)


        ld a,1			;these two put a pixel at bit 7
        ld ($FC00), a		;of byte 1 of the video mem


Wait:


        call GET_KEY	;I wanted to check the keypad
        cp 0		;compare the a reg with 0	
        JUMP_Z(Wait)	;if zero flag gets set, loop back (no keypress)


        ret z		;return to zshell;  (I think my problem is here, 
			;but I took this command from another prgm)
.end




I really would appreciate any input.


TIA


Mark
<pre>
-- 




"No hay mal que por bien no venga" 
 - Spanish proverb


Mark and Esmeralda Lybrand
1330 West 10th Avenue #51
Kennewick WA 99336-6070
USA


Tel: (509) 586-1807
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