DEF SEG Statement
 ----------------------------------------------------------------------------


 Action

 Sets the current segment address for a subsequent  PEEK function,  BLOAD,
 BSAVE,  Absolute routine, or  POKE statement.


 Syntax

  DEF SEG -= address-


 Remarks

 For  Absolute,  BLOAD,  BSAVE,  PEEK, and  POKE,  address is used as the
 segment. The argument  address is a numeric expression with an unsigned
 integer value between 0 and 65,535, inclusive. If you use a value outside
 this range, BASIC generates the error message Illegal function call. The
 previous segment is retained if an error occurs. If  address is omitted,
 DGROUP is used.

  DEF SEG remains in effect until changed. To reset the current segment to
 the default data segment (DGROUP), use  DEF SEG without any argument.

 Be sure to separate  DEF and  SEG with a space. Otherwise, BASIC interprets
 the statement to mean "assign a value to the variable DEFSEG."

 To set the current segment address to the address of data stored in far
 memory, you can use  DEF SEG with the  SSEG or  VARSEG functions ( SSEG
 returns the current segment address of a string;  VARSEG returns the current
 segment address of numeric data). For example, this statement sets the
 current address for a far string named a$ .

 DEF SEG = SSEG(a$)

 When using  DEF SEG in OS-2 protected mode, any  DEF SEG statement must
 refer only to a valid selector. The  DEF SEG statement itself does not
 generate any memory references using the selector, nor does it attempt to
 validate the selector. If a misdirected  DEF SEG statement causes your
 program to refer to an illegal memory address, the operating system may
 generate a protection exception, or BASIC may generate the error message
 Permission denied. The default  DEF SEG segment always constitutes a valid
 memory reference. Use caution when altering this reference in protected
 mode.

 DEF SEG and Expanded Memory Arrays
 Do not use  DEF  SEG to set the segment of
 an expanded memory array. If you start QBX with the -Ea switch, any of these
 arrays may be stored in expanded memory.

   -         Numeric arrays less than 16K in size.

   -         Fixed-length string arrays less than 16K in size.

   -         User-defined-type arrays less than 16K in size.

 If you want to use  DEF  SEG to set the segment of an array, first start QBX
 without the -Ea switch. (Without the -Ea switch, no arrays are stored in
 expanded memory.)

 For more information on using expanded memory, see "Memory Management for
 QBX" in  Getting Started.


 BASICA

 In this version of BASIC, the  CALL and  CALLS statements do not use the
 segment address set by  DEF SEG.


 See Also

  SADD;  SSEG;  VARPTR,  VARSEG


 Example

 The following example uses  DEF  SEG,  PEEK, and  POKE to turn the Caps Lock
 key on and off.

 This program contains hardware-specific instructions. It works correctly on
 IBM PC, XT, and AT computers.

 DECLARE SUB CapsOn ()
 DECLARE SUB CapsOff ()
 DECLARE SUB PrntMsg (R%, C%, M$)
 CLS
 CapsOn
 PrntMsg 24, 1, "<Caps Lock On>"
 LOCATE 12, 10
 LINE INPUT "Enter a string (all characters are caps). ", S$
 CapsOff
 PrntMsg 24, 1, "              "
 PrntMsg 25, 1, "Press any key to continue..."
 DO WHILE INKEY$ = "". LOOP
 CLS
 END

 SUB CapsOff STATIC' Turn the Caps Lock key off.
    DEF SEG = 0' Set segment to low memory.
       POKE &H417, PEEK(&H417) AND &HBF' Turn off bit 6 of &H0417.
    DEF SEG ' Restore segment.
 END SUB

 SUB CapsOn STATIC' Turn Caps Lock on.
    DEF SEG = 0' Set segment to low memory.
       POKE &H417, PEEK(&H417) OR &H40' Turn on bit 6 of &H0417.
    DEF SEG ' Restore segment.
 END SUB

 SUB PrntMsg (Row%, Col%, Message$) STATIC
 ' Print message at Row%, Col% without changing cursor.
    CurRow% = CSRLIN. CurCol% = POS(0)' Save cursor position.
    LOCATE Row%, Col%. PRINT Message$;
    ' Restore cursor.
    LOCATE CurRow%, CurCol%
 END SUB