Q57368: Explanation of Critical Error Codes Returned by ERDEV
Article: Q57368 Product(s): See article Version(s): 2.00 3.00 4.00 4.00b 4.50 Operating System(s): MS-DOS Keyword(s): ENDUSER | SR# S891127-3 B_BasicCom B_GWBasicI | mspl13_basic Last Modified: 17-OCT-1990 ERDEV is an integer function that returns an error code from the last device to declare a critical error. ERDEV is set by the critical error handler, interrupt 24Hex, when DOS detects a critical DOS call error. For block and character device errors, ERDEV will contain the error code from interrupt 24Hex in the lower 8 bits. For block devices only, bit positions 9 to 16 contain device-attribute information which is found in the device-driver header of the device that the error is coming from. The above information applies to Microsoft GW-BASIC versions 3.20, 3.22, and 3.23; to Microsoft QuickBASIC versions 2.00, 3.00, 4.00, 4.00b, and 4.50; to Microsoft BASIC Compiler versions 6.00 and 6.00b for MS-DOS; and to Microsoft BASIC Professional Development System (PDS) versions 7.00 and 7.10 for MS-DOS. When using Microsoft BASIC PDS version 7.00 or 7.10 for MS-DOS, ERDEV can also be set by a time-out error on the communications port and indicates which option in the OPEN COM statement (CD, CS, or DS) is experiencing the time-out. If ERDEV returns an error from a block device (such as a floppy disk drive or fixed disk) or from a character device (such as a terminal or printer), the low byte of ERDEV will return the DOS error code, a value between 0 and 12. The following is a list of these errors: 0 write-protect error 1 unknown unit 2 drive not ready 3 unknown command 4 date error (CRC) 5 bad request structure length 6 seek error 7 unknown media type 8 sector not found 9 printer out of paper 10 write fault 11 read fault 12 general failure 13 reserved 14 reserved 15 invalid disk change (MS-DOS version 3.0 only) For more information on DOS error codes, see INT 24H on Page 481 of "Advanced MS-DOS Programming, 2nd Edition," by Ray Duncan (Microsoft Press, 1988). If the device returning an error is a block device, the high byte of the integer returned by ERDEV will contain device attribute information. This device attribute information comes from the device-attribute word in the device header. The only bits from this word returned by ERDEV are bits 15, 14, 13, XX, 3, 2, 1, and 0, in that order. XX indicates that bits 12 through 4 of the device-attribute word will always return zero. The following is a description of the bits in the device-attribute word that are meaningful to ERDEV: Bit Position Bit Significance -------- --- ------------ 8 15 0 if block device 7 14 1 if IOCTL read and write supported 6 13 1 if BIOS parameter block in boot sector should be used to determine media characteristics 0 if media ID byte should be used 4 3 1 if current CLOCK$ device 3 2 1 if current NUL device 2 1 1 if driver supports 32-bit sector addressing (MS-DOS 4.00) 1 0 1 if current standard input device (stdin) For more information on device-attribute words, see Page 264 of the "Advanced MS-DOS Programming" Microsoft Press book. When using BASIC PDS version 7.00, ERDEV also returns information for COM time-out errors in the low byte. If there is a time-out, ERDEV is set to a value that indicates the signal line that timed out, according to the following table: ERDEV Value Signal Line ----------- ----------- 128 Clear to Send (CTS) timeout 129 Data Set Ready (DSR) timeout 130 Data Carrier Detect (DCD) timeout The following program lines generate the DOS and COM time-out error codes (low byte) and device attribute information (high byte): x= ERDEV DosErrCode = x AND &HFF 'Low byte of ERDEV DevAttr = (x AND &HFF00) \256 'High byte of ERDEV The following example prints the values of ERDEV after the program tries to OPEN a read only file for OUTPUT: Example ------- DEFINT A-Z ON ERROR GOTO ErrorHandler OPEN "C:\TheFile.DAT" FOR OUTPUT A #1 'TheFile is a read-only 'file END ErrorHandler: x = ERDEV DosErrCode = x AND &HFF 'low byte of ERDEV PRINT "The DOS error code returned by ERDEV => "; x RESUME NEXT
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