#include "ti86asm.inc"

.org _asm_exec_ram

Begin:
	call _getkey
	cp kAdd 		;cp I guess is like saying check if something is happening kAdd is the plus 
					;so what this is saying is to check if the plus key is being pressed
	jr z,Acon		;This is going to jump to the contrast increase routine if the plus key is 
					;pressed. If it is not pressed it will continue in the loop.Pretend that the
					;plus key is the number 3. When you say cp kAdd it is loading the value of
					;that key into an area of memory and if you press the plus key it subtracts 
					;3 so it sets the zero flag and allows you to jump.
	cp kSub			;this is checking if the minus key is pressed
	jr z,Scon		;this is the jump if the minus key is pressed
	cp kExit		;check the exit key
	jr z,End		;jump if exit key is pressed
	jr Begin		;jump no matter what to the beginning
Acon:
	ld a,($C008)	;this is loading the value of the current contrast settings into a register
					;so that you can manipulate it. If you just loaded a number in it, it would
					;destroy the current settings, so it usually is helpful keep the current 
					;value.
	inc a			;this adds 1 to the value at $C008 which, in turn, will darken the contrast
					;but can only do so after you reload it back into the memory address that 
					;controls the contrast
	ld ($C008),a	;this is where you put the new value back in the contrast memory address
	out (2),a		;this ouputs the new value in memory to port 2, which is the contrast
	jr Begin		;this jumps you back to the original loop
	
Scon:
	ld a,1
	ld a,($C008)	;loads current contrast settings into a register
	sbc a,1			;subtracts 1 from a
	ld ($C008),a	;loads the new value back in
	out (2),a		;this outputs to the video port
	jr Begin		;jumps to original loop
End:
	ret				;will return to the calling program. If I would have pust call z,end instead
					;of jr end this would just put you back in the original loop, but because of 
					;the fact that when you run an assembly program It's just like doing a call
					;command except it is from the calcs operating system so it returns to the
					;program it is called from last and that is the operating system so it ends
					;the program
.end