Cracker Handbook 1.0 part 62 ppsx

5H FUNCTION Use: To sequentially write and FCB file. Call registers: AH = 15H DS:DX = Pointer to an FCB already opened. Return registers: AL = 00H if there were no errors, otherwise it will contain the error code: 1 full disk or read-only file, 2 error on the formation or on the specification of The 15H function dates the FCB after writing the register to the present block. 16H FUNCTION Use: To create an FCB file. Call registers: AH = 16H DS:DX = Pointer to an already opened FCB. Return registers: AL = 00H if there were no errors, otherwise it will contain the 0FFH value. It is based on the information which comes on an FCB to create a file on a disk. 21H FUNCTION Use: To read in an random manner an FCB file. Call registers: AH = 21H DS:DX = Pointer to and opened FCB. Return registers: A = 00H if there was no error, otherwise AH will contain the code of the error: 1 if it is the end of file, 2 if there is an FCB specification error and 3 if This function reads the specified register by the fields of the actual block and register of an opened FCB and places the information on the DTA, Disk Transfer Area. 22H FUNCTION Use: To write in an random manner an FCB file. Call registers: AH = 22H DS:DX = Pointer to an opened FCB. Return registers: AL = 00H if there was no error, otherwise it will contain the error code: 1 if the disk is full or the file is an only read and 2 if there is an error on the It writes the register specified by the fields of the actual block and register of an opened FCB. It writes this information from the content of the DTA. 3CH FUNCTION Use: To create a file if it does not exist or leave it on 0 length if it exists, Handle. Call registers: AH = 3CH CH = File attribute DS:DX = Pointer to an ASCII specification. Return registers: CF = 0 and AX the assigned number to handle if there is no error, in case there is, CF ill be 1 and AX will contain the error code: 3 path not found, 4 there This function substitutes the 16H function. The name of the file is specified on an ASCII chain, which has as a characteristic being a conventional chain of bytes ended with a 0 character. The file created will contain the attributes defined on the CX register in the following manner: Value Attributes 00H Normal 02H Hidden 04H System 06H Hidden and of system The file is created with the reading and writing permissions. It is not possible to create directories using this function. 3DH FUNCTION Use: It opens a file and returns a handle. Call registers: AH = 3DH AL = manner of access DS:DX = Pointer to an ASCII specification Return registers: CF = 0 and AX = handle number if there are no errors, otherwise CF = 1 and AX = error code: 01H if the function is not valid, 02H if the file was not found, 03 The returned handled is 16 bits. The access code is specified in the following way: BITS 7 6 5 4 3 2 1 . . . . 0 0 0 Only reading . . . . 0 0 1 Only writing . . . . 0 1 0 Reading/Writing . . . x . . . RESERVED 3EH FUNCTION Use: Close file (handle). Call registers: AH = 3EH BX = Assigned handle Return registers: CF = 0 if there were no mistakes, otherwise CF will be 1 and AX will contain the error code: 06H if the handle is invalid. This function dates the file and frees the handle it was using. 3FH FUNCTION Use: To read a specific quantity of bytes from an open file and store them on a specific buffer. 5.4.2 10h Interruption Purpose: To call on diverse BIOS video function Syntax: Int 10H This interruption has several functions, all of them control the video input/output, to access each one of them it is necessary that the function number which is required at the moment of calling the interruption is in the Ah register. In this tutorial we will see some functions of the 10h interruption. Common functions of the 10h interruption 02H Function, select the cursor position 09H Function, write attribute and character of the cursor 0AH Function, write a character in the cursor position 0EH Function, Alphanumeric model of the writing characters 02h Function Use: Moves the cursor on the computer screen using text model. . code is specified in the following way: BITS 7 6 5 4 3 2 1 . . . . 0 0 0 Only reading . . . . 0 0 1 Only writing . . . . 0 1 0 Reading/Writing . . . x . . . RESERVED 3EH FUNCTION . CF = 0 and AX = handle number if there are no errors, otherwise CF = 1 and AX = error code: 01 H if the function is not valid, 02 H if the file was not found, 03 The returned handled is 16 bits functions of the 10 h interruption. Common functions of the 10 h interruption 02 H Function, select the cursor position 09 H Function, write attribute and character of the cursor 0AH Function,