assembly 8086 multiply even elements and data segment - arrays

Question

As a part of my homework I need to initialize two one dimensional arrays, every with 10 2B terms, to multiply every even term with 2. I found some codes, but I dont understand part of initializing arrays in memory.
In next part of example, after this queastion, what does it mean MOV AX,PODACI?
does it moves only address of first term in array TABELA and TABELA1 in AX
or it moves first element in array TABELA and TABELA1 in AX (would that be possible in my case, because of size of AX, I have dw type of data?)
Is it necessarry to define only arrays in DATA SEGMENT if address is used as in question above (I need to find max and min element and according to that plan to define also min_niz1 dw ? and max_niz1 dw ? in data segment, is that possible if I am using MOV AX,PODACI)?
What does it mean MOV SI, OFFSET TABELA and MOV DI, OFFSET TABELA1, would that move offset address in SI and DI and what will be in AL and BL later?
:
PODACI SEGMENT 'DATA'
TABELA DB 3Fh, 06h, 5Bh, 4Fh, 66h, 6Dh, 7Dh, 27h, 7Fh, 6Fh
TABELA1 DB 3Fh, 05h, 5Bh, 04h, 03h, 6Dh, 7Dh, 27h, 01h, 6Fh
PODACI ENDS
PROGRAM SEGMENT 'CODE'
ASSUME CS:PROGRAM,DS:PODACI
START: MOV AX,PODACI
MOV DS,AX
MOV SI,0
MOV DI, 0
MOV CX, 10
MOV SI, OFFSET TABELA
MOV DI, OFFSET TABELA1
petlja: MOV AL, [SI]
MOV BL, [DI]
CMP AL, BL
JNZ nije
INC DX
nije: INC SI
INC DI
loop petlja
PROGRAM ENDS
END START
As second part, I need to multiply even terms in arrays with 2, is that possible with this part of code which is below?
mov ax,niz1[di]
add ax,ax
mov niz1[di],ax
I dont know is that correct way to use only even terms of array, and to put back new value in my array?
I tried to execute this with emu 8086 but solution is not obvious for me.
even:
MOV DI, 0
mov ax,niz1[di]
add ax
mov niz1[di],ax
inc di
inc di
cmp di,11
jle even:

Answer 1

The program you studied
In next part of example, after this queastion, what does it mean MOV AX,PODACI?
The pair of instructions
mov ax, PODACI
mov ds, ax
is used to setup the DS segment register so that it points at your program's DATA section.
What does it mean MOV SI, OFFSET TABELA and MOV DI, OFFSET TABELA1, would that move offset address in SI and DI and what will be in AL and BL later?
MOV SI, OFFSET TABELA
MOV DI, OFFSET TABELA1
will load SI and DI with the offsets to both arrays, offsets within the DATA section.
MOV AL, [SI]
MOV BL, [DI]
will load AL and BL each with one byte-sized element of each array.
Your task
I need to initialize two one dimensional arrays, every with 10 2B terms, to multiply every even term with 2
To initialize your new arrays with 10 2B terms, you would use the DW directive:
niz1 dw 100,200,300,400,500,600,700,800,900,1000
The subscripts for all the elements in this array are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
The even terms are those elements that have array subscripts that are even, so the array elements 0, 2, 4, 6, 8.
Because each array element occupies 2 bytes in memory, the offsets where you'll find these elements are 0, 4, 8, 12, 16. Remember that in assembly programming the value that appears between the square brackets (niz1[di]) is an offset in memory and not an array subscript like in high level programming languages.
xor di, di ;Similar to "MOV DI,0".
Even:
shl niz1[di], 1 ;Doubles this element.
add di, 4 ;Goes to next 'even' term.
cmp di, 20 ;Total size of the array.
jb Even ;Repeat as long as we're IN the array.
Please note that your solution to multiply even terms in arrays with 2
mov ax,niz1[di]
add ax !!! typo?
mov niz1[di],ax
is fine, but doubling through shifting to the left is better.
Good luck turning this into a working program.
(Every program needs an exit to the OS, here it's DOS...)