A simple TASM program to display 'a' character on the screen...
.model tiny
.code
MAIN:
MOV AH, 02h ; function 02H to display a character
MOV DL, 'a' ; load a character('a') or ASCII(97) value to DL
INT 21H ; DOS Interrupt
MOV AX, 4C00H ;
INT 21H ; exit
END MAIN
