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Objective

Due September, 16th 2008

Write a program that swaps the upper and lower 4 bits in a byte. For example if the input byte has a value of $D8 the result should be $8D. The input byte should be loaded into Accu A and the result should also be contained in Accu A. Write the program like a subroutine ending in RTS like the block fill examples. Look at the command set of the HC12 processor in particular bit-shift operations to accomplish the task. Each entry must be an individual contribution.

***********************************************************************************
*	Program to swap first four and last four bits of an eight bit byte  	  *
*	Example Given in Class September 11, 2008, EE 3362, Michael Giesselman    *
***********************************************************************************
 
	ORG $1000	; Assembler Directive
 
	LDAA #$C9	; Load ACCU A with $C9
	LDAB #$C9	; Load ACCU B with #c9
 
	LSRA		; Shift ACCU A to the right 1 bit
	LSRA		; Shift ACCU A to the right 1 bit
	LSRA		; Shift ACCU A to the right 1 bit
	LSRA		; Shift ACCU A to the right 1 bit
 
	LSLB		; Shift ACCU B to the left 1 bit
	LSLB		; Shift ACCU B to the left 1 bit
	LSLB		; Shift ACCU B to the left 1 bit
	LSLB		; Shift ACCU B to the left 1 bit
 
	STAA $1050	;
	ORAB $1050	; OR register A with register B
 
	RTS

Alternate Solution

***********************************************************************************
*	Program to swap first four and last four bits of an eight bit byte  	  *
*	Example Given in Class September 16, 2008, EE 3362, Michael Giesselman    *
***********************************************************************************
 
	ORG  $1000		; Assembler Directive
 
	LDAA #$C9		; Load ACCU A with $C9
	LDAB #$C9		; Load ACCU B with $C9
 
	LDX #4			; Load X with 4
 
LOOP:	LSRA			; Logical Shift Right ACCU A
	LSLB			; Logical Shift Left ACCU B
 
	DBNE X,		Loop
 
	STAA $0850
	ORAB $0850
 
 
	RTS

Tools and Resources

• Simulator for 68HC12 (FREE)
• MiniIDE "Devel Environment" (FREE)
• HCS12 Register List/Reference (Compliments of Michael Giesselman)
• Our text book, "The HCS12/9S12" also contains a good list of registers in "Appendix D"

MiniIDE Fudgings

If you are having trouble with the MiniIDE giving an error like A2003, "can't find asm12.exe," or every line of your program has an error here are a few things to try before pulling your hair or asking the professor.

1. Make sure that the MiniIDE is actually pointing to asm12.exe. This should fix most of the "file not found" and "Error A2003" type issues. You can check this by opening the MiniIDE, clicking "build" in the top menu, then selecting "options." Once the "Options" dialog opens, select the tab that says "Tools." Now you should see a text field labeled "Assembler." Click the button that looks like ">>" and browse to the folder in which you installed MiniIDE, mine was "C:\Program Files\MGTEK\MiniIDE" and select the file titled "asm12.exe" and click "open."
2. When you first save a new code document in MiniIDE be sure to save it with a *.asm extension. You shouldn't have to do this, but on my system at least, MiniIDE is not including this and asm12.exe (the assembler) seems to want the extension or at a minimum the meta data for the file type.
3. Also, be sure that you place a tab in front of the commands like in the code example above. If you don't MiniIDE may throw an error for every executable line of code in your program. You should pay particular close attention to this issue, especially when copying and pasting code.