Write a program called UNPACK to convert the 16bit BCD varia

Write a program called UNPACK to convert the 16-bit BCD variable in memory locations 0x40001000 and 0x40001001 to four ASCII characters with the high-order digit first, beginning in memory location 40001004H.

use the Keil assembler discussed in class and use the program shell from Assembly2.s as a starting point for each program.

   AREA   Assembly1, CODE, READONLY
   EXPORT   __main
__main  
   ENTRY
mystart   LDR r3,= 0x40001000   ;point to RAM location
;
;************************************************************************
; For other programs (projects) replace the code below with new code.
; Leave the code outside the ******* lines as is for all programs.
; begin initialize data
       LDR r4,= 0x25       ;set first operand = 0x100
       LDR r5,= 0x50       ;set second operand to 0x50
       STRB r4,[r3,#0]       ;write first operand to memory
       STRB r5,[r3,#1]       ;write second operqand to memory
; end initialize data
       LDRB r0,[r3,#0]       ;get first operand
       LDRB r1,[r3,#1]       ;get second operand
       ADD   r2,r0,r1       ;form the sum of the two values
       STRB r2,[r3,#2]       ;save sum
;        STRB r2,[r3,#3]       ;save sum
;************************************************************************
;
; an infinite loop because the processor continues to fetch instructions
stop   BAL   stop
   END           ;END directive to show nothing more in file
  
  

Solution

1. Write a program called UNPACK to convert the 16-bit BCD variable in memory locations 0x40001000 and 0x40001001 to four ASCII characters with the high-order digit first, beginning in memory location 40001004H.
(0x40001000H) = 58
Result = (0x40001001) = 08 and
(40001004H) = 05
Source program
LDA 0x40001000H: Get the packed BCD number
ANI FOH : Mask lower nibble
RRC
RRC
RRC
RRC : Adjust higher BCD digit as a lower digit
STA 0x40001001: Store the partial result
LDA 40001004H: .Get the original BCD number
ANI OFH : Mask higher nibble
STA 40001004H: Store the result
HLT : Terminate program execution