Question

Write a program segment to copy a table with five items from a memory location starting at $5000 to a memory location starting at $6000.

Answer 1

Algorithm –

1. set the value of offset SI equal to 5000.
2. set the value of offset DI equal to 6000.
3. load the value 0000 into register AX.
4. load the data of AX register into DS(data segment).
5. load the data of AX register into ES(extra segment).
6. load the data of offset SI into CL register and load value 00 into CH register.
7. increment the value of SI by one.
8. clear the directional flag so that data is read from lower memory to higher memory location.
9. check the value of CX, if not equal to zero then repeat step 10 otherwise go to step 11.
10. transfer the data from source memory location to destination memory location and decrease the value of CX by one.
11. Stop.

ADDRESS	MNEMONICS	COMMENTS
0400	MOV SI, 5000	SI<-5000
0403	MOV DI, 00	DI<-6000
0406	MOV AX, 0000	AX<-0000
0409	MOV DS, AX	DS<-AX
040B	MOV ES, AX	ES<-AX
040D	MOV CL, [SI]	CL<-[SI]
0410	MOV CH, 00	CH<-00
0412	INC SI	SI<-SI+1
0413	CLD	Clears the directional Flag
0414	REP	repeat until CX is not equal to zero and CX=CX-1 at every step
0415	MOVSB	transfer the data from source to destination memory location
0416	HLT	end

Explanation:-

MOV SI, 5000: load the value 5000 into offset SI.

MOV DI, 6000: load the value 6000 into offset DI.

MOV AX, 0000: load the value 0000 into AX register.

MOV DS, AX: load the value of AX register into DS (data segment).

MOV ES, AX: load the value of AX register into ES (extra segment).

MOV CL, [SI]: load the data of offset SI into CL register.

MOV CH, 00: load value 00 into CH register.

INC SI: increment the value of SI by one.

CLD: clears the directional flag i.e. DF=0.

REP: repeat until value of CX is not equal to zero and decrement the value of CX by one at each step.

MOVSB: transfer the data from source memory location to destination memory location.

HLT: end.