1571-10.TXT rev 1a 96-11-06
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
     THIS DOCUMENT IS COPYRIGHT (C) 1988, 1996 BY HERNE DATA
     SYSTEMS LTD.  THE MATERIAL CONTAINED HEREIN MAY BE FREELY
     USED FOR PERSONAL INFORMATION ONLY.  IF YOU REPRODUCE IT,
     THIS COPYRIGHT NOTICE MUST NOT BE REMOVED.  THIS MATERIAL
     MAY NOT BE EXPLOITED FOR COMMERCIAL PURPOSES.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Herne Data Systems Ltd., 
PO Box 250, Tiverton, ON N0G 2T0 CANADA.  
Voice/fax 519-366-2732, 
e-mail herne@herne.com, 
internet: http://www.herne.com

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *


                    AUTO BOOTING on the C-128
                    with a 1541 or 1571 Drive



The C-128 has the ability to automatically load and run either a
machine language or BASIC program from disk when it is first 
turned on or the reset button is pressed.  In this process, known
as AUTOBOOTING, the computer loads track 1, sector 0 into memory 
at address 2186 in bank 0 (part of the BASIC stack area) and 
checks it for a certain combination of bytes.  If the byte 
pattern is matched, the machine language instructions in the 
remainder of the sector are executed.  This feature works with 
both the 1571 and 1541 disk drives, as well as with most other 
compatible Commodore and non-Commodore drives.


For AutoBooting, the first three bytes of track 1, sector 0 must 
be the characters "CBM" followed by four CHR$(0)s.  This can be 
followed by an optional message to be displayed during boot-up of
up to 16 characters.  The message is followed by two more 
CHR$(0)s.  This sequence is followed by some machine language 
instructions and a BASIC command string consisting of either 
RUN"filename" or BOOT"filename" for BASIC or macine language 
programs, respectively.  The final byte is another CHR$(0).  The 
machine language instructions are:

         LDX #address low
         LDY #address high
         JMP AEA5

where address low and address high are the low and high bytes of 
the beginning of the RUN or BOOT string that follows.  This 
address may change depending on the length of the boot message 
string.  The JMP instruction goes to the area of ROM for handling
BASIC commands.



Listing one, AUTOBOOT MAKER is a short BASIC 7 program which 
allows you to write the required byte pattern to make a boot 
disk.  One word of caution, however.  Since the program uses the 
random disk block write method to write the boot sector, the boot
disk should not be subjected to the DOS VALIDATE or BASIC 7 
COLLECT command.  Either of these commands may cuase the boot 
sector to be overwritten and in any case will cause it to become 
un-allocated.  AUTOBOOT MAKER will warn you if it finds track 1, 
sector 0 already allocated.  If you get such a message, you can 
either overwrite the existing sector or try another disk.  If the
disk already has a boot sector written, the old data will be 
replaced by the new.  In any event, it is perhaps better to write
a boot sector on a new disk immediately after formatting it.  
This ensures that the sector does not have any valid data on it.



Interestingly, the BASIC command string used in the boot sector 
is not limited to BOOT"filename" or RUN"filename", but can be any
valid immediate mode BASIC command.  By changing lines 70 and 80 
of the program to contain the appropriate command string such as:

  70 BO$=BO$+"DIRECTORY"+CHR$(0)

you could have an automatic display of the disk directory on boot
up.  Other useful applications include DLOADing a program 
(without running it); BLOADing a machine language utility, sprite
data, function key definitions, custom title screen, etc.; or 
perhaps merely changing the screen colors with a couple of COLOR 
commands.  The only apparent restriction on the command string is
that its total length must be less than one BASIC line and must 
contain only one logical line (i.e. no CHR$(13)s).  All 
statements must be immediate mode (i.e. INPUT, GET etc. are not 
allowed).



Of course, most of the above applications (except for the DLOAD) 
can be performed by a RUN"filename" type command string.  
However, while these programs are easily accessible to prying 
eyes from the disk directory, a person needs a disk sector editor
to view or change the contents of a custom boot sector command 
string.



LISTING One:

10 BO$="CBM":C0$=CHR$(0):FORI=1TO4:BO$=BO$+C0$:NEXT:COLOR0,7:COLOR4,7:PRINT"  "

20 PRINT"BOOT MESSAGE":INPUT" MAX 16 CHARS";ME$:ME$=LEFT$(ME$,16): SA=2831+LEN(ME$)

30 INPUT" BOOT FILE NAME";BF$:INPUT" {B}ASIC OR {M}ACH. LANG.";FT$:PRINT" "

40 PRINT"  BOOT MESSAGE:  "ME$:PRINT" BOOT FILE NAME:  "BF$;: 
   IFFT$="M"THENPRINT"  MACH. LANG.":ELSEPRINT"  BASIC"

50 INPUT"  OK {Y/N}";O$:IFO$<>"Y"THEN10

60 BO$=BO$+ME$+C0$+C0$+CHR$(162)+CHR$(SA AND255)+CHR$(160)+ 
   CHR$(SA/256)+CHR$(76)+CHR$(165)+CHR$(175)

70 IFFT$="M"THENBO$=BO$+"BOOT":ELSEBO$=BO$+"RUN"

80 BO$=BO$+CHR$(34)+BF$+CHR$(0):OPEN15,8,15:OPEN8,8,8,"#":IFDSTHENDCLOSE:GOTO110

90 PRINT#15,"U1:";8;0;1;0:PRINT#15,"B-A:";0;1;0:IFDS=65THEN120

100 PRINT#15,"B-P:";8;0:PRINT#8,BO$;:PRINT#15,"U2:";8;0;1;0:DCLOSE:
    IFDSTHEN110:ELSEEND

110 PRINT"  DISK ERROR  >>  ";DS$:GOTO40

120 PRINT"  BOOT SECTOR ALREADY IN USE":INPUT"  OVER-WRITE {Y/N}";OW$: 
    IFOW$="Y"THEN100:ELSE40