Subtract two 16-bit numbers

Statement: Subtract the 16-bit number in memory locations 4002H and 4003H from the 16-bit number in memory locations 4000H and 4001H. The most significant eight bits of the two numbers are in memory locations 4001H and 4003H. Store the result in memory locations 4004H and 4005H with the most significant byte in memory location 4005H.

Sample problem: (4000H) = 19H (400IH) = 6AH (4004H) = I5H (4003H) = 5CH Result    = 6A19H - 5C15H = OE04H (4004H) = 04H (4005H) = OEH Source program: LHLD 4000H : Get first 16-bit number in HL XCHG : Save first 16-bit number in DE LHLD 4002H : Get second 16-bit number in HL MOV A, E : Get lower byte of the first number SUB L : Subtract lower byte of the second number MOV L, A : Store the result in L register MOV A, D : Get higher byte of the first number SBB H : Subtract higher byte of second number with borrow MOV H, A : Store l6-bit result in memory locations 4004H and 4005H. SHLD 4004H : Store l6-bit result in memory locations 4004H and 4005H. HLT : Terminate program execution.