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Need help in LC# code

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qaizaar

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Need help in LC# code

Nov 5th, 2006

how do i read an input in LC-3 where it checks for yes or no as an answer to a prompt and returns 1 if yes and no if 0. thanks

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Ancient Dragon Ancient Dragon is offline

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Re: Need help in LC# code

Nov 6th, 2006

you should probably get the recommended book Introduction to Computing Systems: From Bits and Gates to C and Beyond and read it. I don't know the first thing about it, so can't help you.

Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.

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c0dex

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Re: Need help in LC# code

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Dec 4th, 2008

You're just in luck. I just finished writing a similar subroutine for my assembly class (uses the same textbook as mentioned above) to ask if someone wants to play again (we've made the game pong breakout). The following code is documented well enough for you to understand it clearly.

 Help with Code Tags 
 Assembly Syntax (Toggle Plain Text) 
; 
; Prompts the user for something.
; 
; Preconditions:
; 
;     TRAP x42 must be implemented in the OS in a way that it does not wait
;     for a key to be pressed. It should only check if a key's pressed once.
;
;	Must use the following declarations.
;
;	PROMPT .STRINGZ "Would you like to do something (y/n)? "
;	HEX_Y1 .FILL x79			; hex for 'y'
;	HEX_Y2 .FILL x59			; hex for 'Y'
;	HEX_N1 .FILL x6E			; hex for 'n'
;	HEX_N2 .FILL x4E			; hex for 'N'
; 
; Postconditions:
; 
;	If yes, return 1 in R0.
;	If no, return 0 in R0.
; 
PROMPT_SR
	LEA R0, PROMPT			; Load PROMPT to R0 be a string.
	TRAP x22				; Print the string in R0.
 
POLL	TRAP x42 				; Get the key press. (This code assumes that
						; TRAP x42 does not wait for a key to be pressed.
 
	LD R4, HEX_Y1			; Load the hex value for 'y'.
	NOT R4, R4;				; Get the 2's compliment 
	ADD R4, R4, #1			;
	ADD R4, R5, R4			; R4 = R5 - R4
 
	BRz YES				; If R5 is zero, then 'y' was pressed.
 
	LD R4, HEX_Y2			; Load the hex value for 'Y'.
	NOT R4, R4;				; Get the 2's compliment 
	ADD R4, R4, #1			;
	ADD R4, R5, R4			; R4 = R5 - R4
 
	BRz YES				; If R5 is zero, then 'Y' was pressed.
 
	LD R4, HEX_N1			; Load the hex value for 'n'.
	NOT R4, R4;				; Get the 2's compliment 
	ADD R4, R4, #1			;
	ADD R4, R5, R4			; R4 = R5 - R4
 
	BRz NO				; If R5 is zero, then 'n' was pressed.
 
	LD R4, HEX_N2			; Load the hex value for 'N'.
	NOT R4, R4;				; Get the 2's compliment 
	ADD R4, R4, #1			; 
	ADD R4, R5, R4			; R4 = R5 - R4
 
	BRz NO				; If R5 is zero, then 'N' was pressed.
 
	BRnzp POLL				; y/Y or n/N has not bee pressed, so poll again.
 
YES:
	AND R0, R0, #0			; Clear R0.
	ADD R0, R0, #1			; Add one to R0.
	RET
 
NO:	
	AND R0, R0, #0			; Clear R0.
	RET
; 
; Prompts the user for something.
; 
; Preconditions:
; 
;     TRAP x42 must be implemented in the OS in a way that it does not wait
;     for a key to be pressed. It should only check if a key's pressed once.
;
;	Must use the following declarations.
;
;	PROMPT .STRINGZ "Would you like to do something (y/n)? "
;	HEX_Y1 .FILL x79			; hex for 'y'
;	HEX_Y2 .FILL x59			; hex for 'Y'
;	HEX_N1 .FILL x6E			; hex for 'n'
;	HEX_N2 .FILL x4E			; hex for 'N'
; 
; Postconditions:
; 
;	If yes, return 1 in R0.
;	If no, return 0 in R0.
; 
PROMPT_SR
	LEA R0, PROMPT			; Load PROMPT to R0 be a string.
	TRAP x22				; Print the string in R0.

POLL	TRAP x42 				; Get the key press. (This code assumes that
						; TRAP x42 does not wait for a key to be pressed.

	LD R4, HEX_Y1			; Load the hex value for 'y'.
	NOT R4, R4;				; Get the 2's compliment 
	ADD R4, R4, #1			;
	ADD R4, R5, R4			; R4 = R5 - R4
	
	BRz YES				; If R5 is zero, then 'y' was pressed.

	LD R4, HEX_Y2			; Load the hex value for 'Y'.
	NOT R4, R4;				; Get the 2's compliment 
	ADD R4, R4, #1			;
	ADD R4, R5, R4			; R4 = R5 - R4
	
	BRz YES				; If R5 is zero, then 'Y' was pressed.

	LD R4, HEX_N1			; Load the hex value for 'n'.
	NOT R4, R4;				; Get the 2's compliment 
	ADD R4, R4, #1			;
	ADD R4, R5, R4			; R4 = R5 - R4
	
	BRz NO				; If R5 is zero, then 'n' was pressed.

	LD R4, HEX_N2			; Load the hex value for 'N'.
	NOT R4, R4;				; Get the 2's compliment 
	ADD R4, R4, #1			; 
	ADD R4, R5, R4			; R4 = R5 - R4
	
	BRz NO				; If R5 is zero, then 'N' was pressed.

	BRnzp POLL				; y/Y or n/N has not bee pressed, so poll again.

YES:
	AND R0, R0, #0			; Clear R0.
	ADD R0, R0, #1			; Add one to R0.
	RET

NO:	
	AND R0, R0, #0			; Clear R0.
	RET