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Apparatus Used: Microprocessor Kit, Keyboard
Assumption: We have to write a program to subtract two 16 bit numbers. In this case for any 16 bit number, lower byte takes a location and also higher byte take a location, same for the second number and also for output, so we use 6 memory locations for this.
Algorithm:
  • Load First number at given location
  • Store first number in D-E pair
  • Load Second Number
  • Store content of E in Accumulator
  • Add L and E and store output in L
  • Move D in Accumulator
  • Subtract H and D and store output in H
  • Store content of H and L at given location
  • End the Program
Program:
Memory Address
Op-code
Operand
Comments
2000
LHLD
2050 H
Get First Number
2003
XCHG

Save Ist Number in D-E pair
2004
LHLD
2052 H
Get  2nd No in H-L pair
2007
MOV
A,E
Save data of E in A  
2008
SUB
L
Subtract E-L
2009
MOV
L,A
Store output in L
200A
MOV
A,D
Move D into A
200B
SBB
H
Subtract H from D
200C
MOV
H,A
Store output into H
200D
SHLD
2054
Store Final Output
2010
RST
5
Set Break-point
2011
END

End the program

Used Instruction:
LHLD addr: This instruction copies the contents of memory location given within the instruction into L register and contents of next memory location into the H register.
XCHG: Exchange the Contents of H with D and L with E.
MOV rd, rs: This instruction copies data from the source register into destination register.
SUB r: This instruction subtract the content of specified register from the contents of accumulator and store result in the accumulator.
SBB r: This instruction will subtract the content of specified register from content of accumulator with carry.
SHLD: The contents of register L are stored in the memory location specified by the 16-bit address in the operand and the contents of register H are stored in the next memory location.
RST 5: This instruction is used to set break-point for the execution.
END: This instruction is used to execute the program.

Result:
Input:
First Number-2345
2nd Number-1234
Store as
2050-45
2051-23
2052-34
2053-12
Output:
2054-11
2055-11
Procedure to look output
  • After press ENTER, You will get first screen
  • Press G and Provide Initial address (as 2000)
  • Press SHIFT+4,You will get first screen again
  • Press M and Provide Input location for Input (M2050)
  • Press ENTER and Provide your Input at location (2050:45)
  • Press ENTER and Provide your Input at location (2051:23)
  • Press ENTER and Provide your Input at location (2052:34)
  • Press ENTER and Provide your Input at location (2053:12)
  • Press SHIFT+4
  • Press G and Provide Initial address (as 2000)
  • Press SHIFT+4,You will get first screen again
  • Press M and Provide address for output (M2054) and press ENTER
  • You will get your desired output.

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