Q59725: INTERRUPT for Clock Tick Counter Returns Negative Value
Article: Q59725 Product(s): See article Version(s): 4.00 4.00b 4.50 Operating System(s): MS-DOS Keyword(s): ENDUSER | SR# S900222-218 B_BasicCom | mspl13_basic Last Modified: 26-MAR-1990 Interrupt 1A Hex, with Function 0, returns the current value of the clock tick counter in registers CX and DX. When the low-order portion of the clock tick counter (returned in DX) exceeds 32,767, it becomes negative when stored as an integer in BASIC, because 32,767 is the maximum value for a 2-byte signed integer. Below is an example to convert the negative value to the equivalent unsigned long integer value. This information applies to Microsoft QuickBASIC Versions 4.00, 4.00b, and 4.50, to Microsoft BASIC Compiler Versions 6.00 and 6.00b, and to Microsoft BASIC Professional Development System (PDS) Version 7.00 for MS-DOS. For a more complete description of converting negative signed integers to unsigned integers, query on the following words: CALL and INTERRUPT and negative and signed and integer The following QuickBASIC program outputs only positive values by removing the sign bit and adding the remaining number plus 1 to 32,767: ' $INCLUDE: 'qb.bi' REM In BASIC 7.00, use $INCLUDE: 'qbx.bi' instead of 'qb.bi'. REM To use CALL INTERRUPT in this program, you must do the following: REM If you run this program in QB.EXE, use QB /L QB.QLB. REM If you run this program in QBX.EXE, use QBX /L QBX.QLB. REM LINK with QB.LIB (or QBX.LIB for BASIC 7.00). DIM inregs AS regtype, outregs AS regtype LOCATE 23, 1: PRINT "Push any key to end program." DO inregs.ax = 0 CALL interrupt(&H1A, inregs, outregs) high& = outregs.cx low& = outregs.dx IF low& < 0 THEN 'if the low-order portion is negative: low& = low& AND &H7FFF 'remove sign bit low& = low& + &H7FFF + 1 'add remaining number plus 1 to 32,767 END IF LOCATE 24, 1: PRINT high&; ":"; low&; " "; LOOP UNTIL INKEY$ <> "" END
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