1. Lecture 6 Presented By Dr. Shazzad Hosain Asst. Prof. EECS, NSU

2. Agenda String Data Transfer Instructions – The Direction Flag – LODS Instructions – STOS Instructions – MOVS Instructions – INS and OUTS Instructions More Examples

3. String Data Transfers Five Instructions – LODS, STOS, MOVS, INS and OUTS Each instruction allows data transfer either a single byte, word or double word

4. The Direction Flag, DF DF = 0, auto-increment mode of SI, DI DF = 1, auto-decrement mode of SI, DI CLD instruction clears the D flag (D = 0) STD instruction sets the D flag (D = 1) SI (Source Index) points to DS (Data Segment) i.e. DS:[SI] DI (Destination Index) points to ES (Extra Segment) i.e. ES:[DI]

5. LODS Instructions LODS instructions loads AL, AX or EAX with data indexed by SI register LODSB – load string byte Table 4-10: from Brey’s book

6. Example STRING1 DB‘ABC’ MOV AX, @DATA MOV DS, AX LEA SI, STRING1 CLD LODSB

7. STOS Instructions STOS instructions stores data form AL, AX or EAX to memory indexed by DI register STOSB – store string byte Table 4-11: from Brey’s book

8. Example STRING1 DB‘HELLO’ MOV AX, @DATA MOV ES, AX LEA DI, STRING1 CLD MOV AL, ‘A’ STOSB

9. REP (Repeat Prefix)) REP is used to execute string instructions repeatedly by CX times. REP automatically decrements CX by 1 REP works for any string instructions except LODS instruction

10. Example : Clear the video text display 12380 **** 1 2 25 ****** 543210543210 abc 07H Video display Text memory cbacba 20H B800H Example 4-5: From Brey’s Book

11. MOVS Instructions MOVSB – move string byte from one memory location to other Table 4-13 : From Brey’s Book

12. Example.DATA STRING1DB ‘HELLO’ STRING1 DB 5 DUP (?) MOV AX, @DATA MOV DS, AX MOV ES, AX LEASI, STRING1 LEADI, STRING2 CLD MOVSB

13. Example: Scroll Up One Line 12380 **** 1 2 25 ****** 543210543210 Video display Text memory B800H Example 4-6: From Brey’s Book 160 **** **** SI DI

14. INS Instructions INSB – Input String Byte, from I/O device to memory location Table 4-14: From Brey’s Book

15. Example Read 50 bytes of data from an I/O device whose address in 03ACH and store the data in LISTS array Example 4-7: From Brey’s Book

16. OUTS Instructions OUTSB – Output String Byte, from string memory location to I/O device Table 4-15: From Brey’s Book

17. Example Transfer data form memory array (ARRAY) to an I/O device at I/O address 3ACH Example 4-8: From Brey’s Book

18. Agenda String Data Transfer Instructions – The Direction Flag – LODS Instructions – STOS Instructions – MOVS Instructions – INS and OUTS Instructions More Examples

19. Concatenate Two Input Strings Then Display Input String 1: Hello Input String 2: World! Concatenated String: Hello World! Display message 1 Read first string Display message 2 Read second string Concatenate the two strings Display the result

20. Display message 1 Read first string Display message 2 Read second string Concatenate the two strings Display the result Display message 1 Read first string

21. Display message 1 Read first string Display message 2 Read second string Concatenate the two strings Display the result Display message 2 Read second string

22. Display message 1 Read first string Display message 2 Read second string Concatenate the two strings Display the result Concatenate the two strings Display the result

23. Mid Term, Fall 2010 October 30, Saturday At 9:00 AM to 10:30 NAC 311

24. References Ch 11, Assembly Language Programming – by Charls Marut Section 4-4, Intel Microprocessors – by Brey