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chkcpu macro
jmp begn msg db 13,10,"This copy of MS-DOS will run only on an 8086",13,10 db "or 8088 CPU based computer. This computer is not ",13,10 db "based on an 8086 or 8088 CPU. ",13,10 db 13,10,"Insert a copy of the appropriate MS-DOS system disk ",13,10 db "and press any key to re-boot.",13,10,0
begn:;------GET_CPU_TYPE------------------------------------------------------------May, 88 by M.Williamson; Returns: AX = 0 if 8086 or 8088; = 1 if 80286; = 2 if 80386; pushf push bx ; preserve bx xor bx, bx ; init bx to zero
xor ax,ax ; 0000 into AX push ax ; put it on the stack... popf ; ...then shove it into the flags pushf ; get it back out of the flags... pop ax ; ...and into ax and ax,0F000h ; mask off high four bits cmp ax,0F000h ; was it all 1's? je scpu_8086 ; aye; it's an 8086 or 8088
mov ax,0F000h ; now try to set the high four bits.. push ax popf pushf pop ax ; ...and see what happens and ax,0F000h ; any high bits set ? jz scpu_286 ; nay; it's an 80286
scpu_386: ; bx starts as zero inc bx ; inc twice if 386scpu_286: ; just inc once if 286 inc bxscpu_8086: ; don't inc at all if 086 mov ax, bx ; put CPU type value in ax pop bx ; restore original bx popf
cmp ax, 0000 je cpu_ok push cs pop ds mov si, offset msgprnt: lodsb or al, al jz prnt_done mov ah, 14 mov bx, 7 int 10h jmp prnt
prnt_done: xor ah, ah int 16h int 19hcpu_ok: endm
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