'A tutorial for Richard Backus' BASICDOS.BAS code.  Here is
'the code in the original form that he sent to me:

'===========>8 CLIP 8<============

'       BASICDOS.BAS
' written: Richard J Backus     27dec95
' purpose: to provide a BASIC BIOS/DOS call interface
' method: using the CALL interface, get registers, call the interrupt, and
'       return the registers. Based on QuickBasic's CALL INTERRUPT routine.
' Warning: Calls requiring segment registers cannot be used.

' QBasic syntax: CALL ABSOLUTE(intnum%, callregs, retregs, VARPTR(asmcode)))
'   intnum%   a valid DOS interrupt number between 0 and 255, type INTEGER
'   callregs  register values required by call, type REGS
'   retregs   register values returned from call, type REGS
TYPE REGS       'Typedef for DOS registers
   ax  AS INTEGER
   bx  AS INTEGER
   cx  AS INTEGER
   dx  AS INTEGER
   bp  AS INTEGER
   si  AS INTEGER
   di  AS INTEGER
   flg AS INTEGER
END TYPE
'       DOS call code
DATA &H55, &H06, &H1E, &H8B, &HEC, &H9C, &H8B, &H7E, &H0E, &H8A
DATA &H05, &H8B, &H7E, &H0C, &HB4, &H35, &HCD, &H21, &H8B, &H46
DATA &HF8, &H05, &H20, &H00, &H0E, &H50, &H06, &H53, &H8B, &H05
DATA &H8B, &H5D, &H02, &H8B, &H4D, &H04, &H8B, &H55, &H06, &H8B
DATA &H6D, &H08, &H8B, &H75, &H0A, &H8B, &H7D, &H0C, &HFA, &HCB
DATA &H1F, &H07, &H57, &H9C, &H8B, &HFC, &H36, &H8B, &H7D, &H0A
DATA &H89, &H05, &H89, &H5D, &H02, &H89, &H4D, &H04, &H89, &H55
DATA &H06, &H89, &H6D, &H08, &H89, &H75, &H0A, &H58, &H89, &H45
DATA &H0E, &H58, &H89, &H45, &H0C, &H5D, &HCA, &H06, &H00
'       Load DOS/BIOS interface routine
DIM dos%(45)                    'get some memory space
DEF SEG = VARSEG(dos%(0))
FOR i% = 0 TO 88
   READ d%
   POKE VARPTR(dos%(0))+i%, d%  'copy code into memory
NEXT i%

'       Message string
DATA &H48, &H65, &H6C, &H6C, &H6F, &H20, &H57, &H6F, &H72, &H6C
DATA &H64, &H0D, &H0A
'       use DOS to output the message
DIM dosregs AS REGS
FOR i% = 0 TO 12
   intnum% = &H21               'parameters for call
   dosregs.ax% = &H200
   READ dosregs.dx%
   DEF SEG = VARSEG(dos%(0))    'set call seg
   CALL ABSOLUTE(intnum%, dosregs, dosregs, VARPTR(dos%(0)))
NEXT i%
END

'=============>8 CLIP 8<================

'TYPE REGS will set up the variable REGS to access all the registers
'you need to make a BIOS call.  This goes in hand with the DIM dosregs
'as REGS.  Dosregs will contain the information of the registers.  For
'example, if you want to send a value to the AX register, you can set
'dosregs.ax=value.  I'm not great at explaining how TYPE works, so best
'consult some books (or the help file) on that one. :)

'Next he has his assembly routine that emulates CALL INTERRUPT.  This
'and the code under it that pokes the routine into memory is the heart
'of the whole thing.

'Next, he creates the data for each character in the string "Hello
'World" and he uses a BIOS video call to place each character on the
'screen (much the same way my GPrint routine does in my GUI interface).
'
'Note how he used CALL ABSOLUTE.  Lets compare it with QB45's CALL
'INTERRUPT syntax:

'QB45:   CALL INTERRUPT (intnum%, dosregs, dosregs)
'QBASIC: CALL ABSOLUTE (intnum%, dosregs, dosregs, VARPTR(dos%(0)))

'Notice all is basically the _same_, you just add the VARPTR at the
'end! And don't forget to change INTERRUPT to ABSOLUTE.  This makes it
'very easy to change a QB45 code to work with QBasic.

'Now, I will try and explain how you can convert QB45 code that uses
'CALL INTERRUPT so that it will work in QBasic.  Of course, you'll need
'the code written by Richard Backus (which was posted in the previous
'message).  Also note this works only for the CALL INTERRUPT calls.  If
'you see CALL INTERRUPTX or CALL INT86, I'm not sure how it will work
'with those, as they take slightly different parameters.

'First off, the QB45 program will have a '$INCLUDE statement in it.
'You must delete that statement.  Next, put the TYPE REGS in AFTER the
'DECLARE SUB and DECLARE FUNCTION statements (if any). You'll want to
'more than likely change REGS to RegType, as that is what the qb.bi was
'using.  This will replace it.

'Now, put the DIM SHARED Inregs as RegType, Outregs as RegType with the
'DIM statements, if there isn't one there already.  Most often than
'not, it may not need changing.  Also add in DIM SHARED dos%(45) and
'DEF SEG = VARSEG(dos%(0)).  It should look something like this:

'DIM and CONST, etc. here
'DIM SHARED Inregs as RegType, Outregs as RegType
'DIM SHARED dos%(45)
'DEF SEG = VARSEG(dos%(0))

'Once you have the variables all set up, next slip the DOS Call Code
'data statements and the Load DOS/BIOS interface routine just before
'the main code of the program starts.  Most of the time, there's a CLS
'or SCREEN statement there.

'Now just one more step.  Look through the code (may want to do a
'search for CALL INTERRUPT).  You will need to change each occurrence of
'INTERRUPT to ABSOLUTE.  And, you will need to add to the end of each
'CALL ABSOLUTE (which was a CALL INTERRUPT) the VARPTR statement.  For
'example, suppose the QB45 code read:

'  CALL INTERRUPT (intnum%, Inregs, Outregs)

'You would change it to read:

'  CALL ABSOLUTE (intnum%, Inregs, Outregs, VARPTR(dos%(0)))

'Be sure to get all the parenthesis right!  There's _3_ of them at the
'end of the ABSOLUTE statement (I say this because I'm bad at it and
'forget a lot! :)

'Now you can save the new code to a new file name (for safe keeping)
'and run it.  It should work!

'If you have any questions, let me know.  I can't promise I'll be able
'to have an answer every time but I'll try.  If you need to contact
'Richard, net mail me and I'll forward your question or whatever to
'him.  Just a short note that he does most of his programming in
'assembly. :)