x86-16

So I'm building a simple 8086 Assembly program that allows the user to input 4 digits, store them in an array and print out the sum of those digits (The sum must be a one digit number): data segment i db ? array db 20 dup(?) sum db ? ends stack segment dw 128 dup(0) ends code segment mov ax, data mov ds, ax mov es, ax mov i, 0 Enter: mov ah, 1 int 21h mov bl, i mov bh, 0 mov array[bx], al inc i cmp i, 4 jne Enter mov sum, 0 mov i, 0 Calc: mov bl, i mov bh, 0 mov al, array[bx] add sum, al inc i cmp i, 4 jne Calc mov dl, sum mov ah, 2 int 21h mov ax, 4c00h int 21h ends However when I input the

I'm trying to understand the MS-DOS v2.0 source code , and in particular some of the code in MSDATA.ASM . This code was originally assembled with a 35+ year old MASM assembler (a version that wasn't commercially available). The code I'm interested in is near the beginning: SUBTTL Initialized data and data used at DOS initialization PAGE ; DATA AREA for MS-DOS IFNDEF KANJI KANJI EQU 0 ;FALSE ENDIF CONSTANTS SEGMENT BYTE PUBLIC 'CONST' EXTRN international_table:BYTE EXTRN Current_Country:WORD ORG 0 CONSTRT EQU $ ; Start of constants segment PUBLIC DevStrLen DEVSTRLEN DB 3 ; Size of below PUBLIC

I am developing an x86 bootloader and have come across this problem (which I guess should be pretty straightforward, but so far I haven't been able to solve): I want to detect the bitness of the CPU host (e.g. if it's 16bit-only, or supports 32bit or 64bit). I have used the CPUID instruction, but it was introduced with 486 so doesn't help for detecting 16-bit-only vs. a 386-compatible CPU that supports 32-bit protected mode (or 32-bit operand-size in real mode with prefixes). Checking for 32-bits (see http://www.rcollins.org/ddj/Sep96/Sep96.html ): 16-bit CPUs without protected mode (8088/8086

We had an activity about looping in assembly language. Our task is simple: display the numbers 0 to 9 with spaces in-between each number. I got the code to work in the command prompt using the 'debug' command in WINDOWS 7 in our school. My laptop is Windows 10 and I recently found out that there's no 'debug' command in the command prompt. So I tried writing my code in DOSBox 0.74 (latest, maybe). Every time i run it in DOSBox, the programs suddenly hangs up and then crashes. Here's the code mov cx,0a mov ah,02 mov dl,30 int 21 mov bl,dl mov dl,20 int 21 mov dl,bl inc dl loop 0107 int 20 Can

I can calculate an address Segment:Offset as Segment * 0x10 + Offset . But how do I calculate the opposite? E.g. how do I get from 0xF4170 to F400:0170 and from 0xACF04 to ABCD:1234 ? Necrolis You would be required to have either the base or the offset to start with, along with the linear address, as multiple Segment:Offset pairs can map to the same linear address. so if we have the segment 0xF400 and the linear address 0xF4170 , we get the offset being 0xF4170 - (0xF400 << 4) which is 0x170 . Doing this with only knowing the linear address doesn't have a unique solution, so you have to choose

I have been trying to draw a box in assembly and move it horizontally across the screen. The code of printing the square itself works for me but when I try to make it move it is not working very well. I can see it moving but not as a full square, if you get my point. My code: in Assembly Tasm STA SEGMENT STACK DB 0FFFeH DUP(?) STA ENDS DATA SEGMENT ;----------- ;VARIABLES HERE xpos dw 50h ypos dw 50h color db 9h constat equ 0ffffh siNum dw ? diNum dw ? numOFtime dw 0h ;------------- DATA ENDS CODE SEGMENT ASSUME CS:CODE,DS:DATA,SS:STA START : MOV AX,DATA MOV DS,AX ;start coding here: mov ah, 0

I'm doing an iso file in assembly and I want to add color to the text (in this case: red). Does anyone know how to do it? [BITS 16] [ORG 0x7C00] jmp main main: mov si, string ; si=string call printstr jmp $ printstr: lodsb ; al=&si[0] cmp al,0 ;FLAGS = 0 jnz print ret print: mov ah,0Eh int 10h jmp printstr string db "HELLO WORLD!",13,10,0 times 510 - ($-$$) db 0 dw 0xAA55 As a preliminary advice, always setup the segment registers that your bootloader depends on. Here, because of lodsb together with [ORG 0x7C00] , you must set DS=0 . Best also make sure the direction flag DF is in a known