1. Data Movement Instructions
A Course in Microprocessor
Electrical Engineering Department
University 17 Agustus 1945 Jakarta

2. Load-Effective Address
There are several LEA instructions in p
Table 4.9 lists the LEA instructions
LEA
The LEA instruction loads a 16- or 32- bit register with the offset address of the data specified by the operand
E.g., LEA AX,NUMB
Compare: LEA BX,[DI] & MOV BX,[DI]
Understand Example 4.3

3. Load-Effective Address (cont’d)
LDS, LES, LFS, LGS, LSS
The LDS, LES, LFS, LGS, LSS instructions load any 16- or 32-bit register with an offset address and load the DS, ES, FS, GS, or SS segment register with a segment address
Fig illustrates an example LDS BX,[DI] instruction
this instruction transfers the 32-bit number, address-ed by DI in the data segment, into the BX and DS registers
Study Example 4.4

4. String Data Transfers
There are 5 string data transfer instructions: LODS, STOS, MOVS, INS, and OUTS
The Direction Flag
The direction flag (D) -located in the flag register- selects the auto-increment (D=O) or the auto-decrement (D=1) operation for the DI and SI registers during string operations
The CLD instruction clears the D flag (D=0), and the STD instruction sets it (D=1)

5. String Data Transfers (cont’d)
DI and SI
The DI offset address accesses data in the extra segment for all string instructions that use it
The SI offset address accesses data, by default, in the data segment
LODS
The LODS instruction loads AL, AX, or EAX with data stored at the data segment offset address indexed by the SI register (Table 4.10)

6. String Data Transfers (cont’d)
Fig.4.16 shows the effect of executing the LODSW instruction if the D flag=0, SI=1000H, and DS=1000H
STOS
The STOS instruction stores AL, AX, or EAX at the extra segment memory location addressed by the DI register
Table 4.11 lists all forms of STOS instructions
The STOSB (stores a byte), STOSW (stores a word) and STOSD (stores a doubleword)

7. String Data Transfers (cont’d)
In example 4.5 STOSW instruction is used to clear the video text display
MOVS
MOVS instruction transfers data (either byte, word or doubleword) from one memory loca-tion to another (Table 4.13)
MOVS transfers data from the data segment location addressed by SI to the extra segment location addressed by DI
Example 4.6 lists a short program that uses MOVS

8. String Data Transfers (cont’d)
INS
The INS (input string) instruction transfers data from an I/O device into extra segment memory location addressed by the DI register
The I/O address is contained in the DX register
See Table 4.14 and Study example 4.7
OUTS
The OUTS (output string) transfers data from the data segment location addressed by SI to an I/O device (addressed by DX) -- Table 4.15 & Example 4.8