Has a jump table entry at $FF53
Entry point for the C64_MODE routine, currently at $E24B
Switches immediately to 64 mode.
Entry point for the BOOT_CALL routine, currently at $F890
Routine needs parameter to be set:
If the specified drive is not present or turned off, or the disk does not contain valid boot sectors, the routine will return carry bit set.
BOOT_CALL routine at $F890 attempts to load and execute the boot sector from an auto-boot disk in the given drive and device. The BOOT protocol is as follows:
On any error, the BOOT operation is aborted and the UI command is issued to the disk. A return may or may not be made to the caller depending upon the completion status and the BOOTed code. The BOOT sector has the following layout:
| $00 | $01 | $02 | $03 | $04 | $05 | $06 | A | B | C | ||
|---|---|---|---|---|---|---|---|---|---|---|---|
| C | B | M | adrl | adrh | bank | blk# | title | 0 | filename | 0 | code |
where: A = $07 + LEN(title)
B = A + LEN(filename)
C = B + 1
The following examples illustrate the flexibility of this layout. This loads and runs a BASIC program:
$00 -> "CBM" $03 -> $00, $00, $00, $00 // no other BOOT sector $07 -> "NAME",$00 // message "NAME" (+ terminator A) $0C -> $00 // no filename (only terminator B) $0D -> // code $A2, $13, // LDX #$13 $A0, $0B, // LDY #$0B $4C, $A5, $AF // JMP $AFA5 (J_EXECUTE_A_LINE) $14 -> RUN"PROGRAM" // BASIC statement $20 -> $00 // empty code (C)
This results in the message Booting NAME… being displayed and, utilizing a C128 BASIC jump table entry that finds and executes a BASIC statement, loads and runs the BASIC program named “PROGRAM”. The same header can be used to load and execute a binary (machine code) program by simply changing RUN to BOOT.
While the file auto-load feature of the boot header could be used to load binary files simply by furnishing a filename, to execute it you must know the starting address and JMP to it. BASIC’s BOOT command does that, and allows a more generic mechanism. In the next example, a menu is displayed and you are asked to select the operating mode. Nothing else is loaded in this “configure”-type header:
$00 -> "CBM" $03 -> $00, $00, $00, $00 // no other BOOT sector $07 -> $00 // no message (only terminator A) $08 -> $00 // no filename (only terminator B) $09 -> // code (C) $20, $7D, $FF, // JSR $FF7D (JPRIMM) $0D, $53, $45, $4C, $45, // String start $43, $54, $20, $4D, $4F, $44, $45, $3A, $0D, $0D, $20, $31, $2E, $20, $43, $36, $34, $20, $20, $42, $41, $53, $49, $43, $0D, $20, $32, $2E, $20, $43, $31, $32, $38, $20, $42, $41, $53, $49, $43, $0D, $20, $33, $2E, $20, $43, $31, $32, $38, $20, $4D, $4F, $4E, $49, $54, $4F, $52, $0D, $0D, $00, // String ends with $0D $20, $E4, $FF, $C9, $31, $D0, $03, $4C, $4D, $FF, $C9, $32, $D0, $03, $4C, $03, $40, $C9, $33, $D0, $EB, $4C, $00, $B0
Starting from $09, the first three bytes stands for
JSR $FF7D
which is a jump to $FF7D (JPRIMM). It prints on screen the string of character codes immediately following the JSR.
So, the code above shows this message and waits for a key press:
SELECT MODE: 1. C64 BASIC 2. C128 BASIC 3. C128 MONITOR
The code after the string (starting with $20 after the $00 in bold):
0000 20 E4 FF JSR $FFE4 0003 C9 31 CMP #$31 // Key code 1 0005 D0 03 BNE $000A (*+3) 0007 4C 4D FF JMP $FF4D // Jump to JC64_MODE 000A C9 32 CMP #$32 // Key code 2 000C D0 03 BNE $0011 (*+3) 000E 4C 03 40 JMP $4003 // Jump to JSOFT_RESET 0011 C9 33 CMP #$33 // Key code 3 0013 D0 EB BNE $0000 (*-15) 0015 4C 00 B0 JMP $B000 // Jump to JMONINIT
The loading of sequential sectors is designed primarily for specialized applications (such as CP/M or games) that do not need a disk directory entry.
Entry point for the SETBNK routine, currently at $F73F
Establishes the current bank from which the data will be read or to which data will be written during load/save operation, as well as the bank where the filename for the I/O operations can be found.
Entry point for the JMPFAR routine, currently at $02E3
Jumps to a routine in a specified bank with no return to calling bank.
Entry point for the SETLFS routine, currently at $F7E8
Assigns the logical file number, device number and secondary address for an I/O operation.
Entry point for the SETNAM routine, currently at $F731
Assigns the length and the address of filename for a I/O operation
If no name is used for this operation, load .A with 0 so .X .Y are irrelevant.
Entry point for the LOAD routine, currently at $F265
Loads or verifies a program file from tape or disk into a specified area of memory.
Entry point for the SAVE routine, currently at $F53E
Saves the contents of a block of memory to disk or tape.