;swap_bytes.asm
;--------------
.STACK
;--------------
.DATA
TEMP DB ? ;DB=define bytes
;$ delimiter meaning end of string
RSLT DB 0DH, 0AH, 'BL = , BH = $'
;--------------
.CODE
BEGIN PROC FAR
;set up pgm ds
MOV AX,@DATA ; place .DATA addr in ax
MOV DS,AX

;assign values to bl and bh
MOV BL,'A'
MOV BH,'B'

;store bl in temp area before swapping
MOV TEMP, BL

;swap registers
MOV BL, BH
MOV BH,TEMP

;move registers to result area for display
MOV RSLT + 7,BL
MOV RSLT + 15,BH

;print result
MOV AH,09H              ;display string
MOV DX, OFFSET RSLT ;rslt address must be in dx
INT 21H                    ;a dos interrupter that uses fctn (?) code in ah

BEGIN ENDP               ;starts pgm at begin (!)
END    

        format  MZ
        entry   MainSeg:BEGIN
        stack   1024

segment MainSeg

BEGIN:
;set up pgm ds
MOV AX,DataSeg ; place .DATA addr in ax
MOV DS,AX

;assign values to bl and bh
MOV BL,'A'
MOV BH,'B'

;swap registers
XCHG BL,BH

;move registers to result area for display
MOV [TheBL],BL
MOV [TheBH],BH

;print result
MOV AH,09H              ;display string
MOV DX,RSLT             ;rslt address must be in dx
INT 21H                 ;a dos interrupter that uses fctn (?) code in ah

MOV AH,4Ch
INT 21h

segment DataSeg

;$ delimiter meaning end of string
RSLT DB 0DH, 0AH, ' BL = '
TheBL DB '?',', BH = '
TheBH DB '?','$'
;--------------
    

Error message : "....\swap_bytes.exe " cannot run due to incompatability with 64-bit versions of windows .

Mr. Revolution, I will try your advice and install the DOSbox and MASM.

I am reading a book called : x86 assembly language and C fundamentals, by J. Cavanagh. I have read the usual basics, and made some small C programs that runs. Now I am on page 200 in the book, and examples proceedes in assembly. And again, equally lost as I were when getting a C program to run, the asm wont run. The book suggests flat assembler. I get errors on every line. Error on capital letters, and error on the "proc far".

I tried to make the capital letters into small letters
and add this include 'win64ax.inc', but no function.

I'm also not sure if you're trying to mix C and assembly or not. FASM doesn't really support that for 16-bit DOS (but 32-bit COFF for DJGPP is okay).

Question. how can it be that many different assemblers run on the same chipset architecture x86, and some codes just doesnt, like the code I have in the book ?

Although, while it isn't technically impossible to step down into a processor mode that can run 16-bit code, the transition would have been too expensive and too much of a hassle to implement.

ok so it would be safe to say that there is an unique assembler "language" for each processor, and for each bit level, like x86, 16bit, 32bit and 64 bit. and there would also be an individual assembly language for the different chips .

The emu8086 is related to fasm, so I presum its relevant for the forum, however maybe not in the DOS thread ? Anybody that is familiar with the emu8086 ?

     .stack
     .data
temp db ?
rslt db 0dh, 0ah, "bl =  , bh =  $" 
;dh = cursor position
;ah = linefeed
;$ = string terminator

     .code
proc
mov ax,@data
mov ds,ax

mov bl,'A'
mov bh,'B'

mov temp,bl

mov bl,bh
mov bh,temp

mov rslt + 7,bl
mov rslt + 15,bh

mov ah,09h
mov dx, offset rslt

int 21h
endp