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

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

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

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]

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

Example STRING1 DB‘ABC’ MOV MOV DS, AX LEA SI, STRING1 CLD LODSB

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

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

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

Example : Clear the video text display **** ****** abc 07H Video display Text memory cbacba 20H B800H Example 4-5: From Brey’s Book

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

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

Example: Scroll Up One Line **** ****** Video display Text memory B800H Example 4-6: From Brey’s Book 160 **** **** SI DI

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

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

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

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

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

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

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

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

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

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

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