C64 JIFFYDOS  Memorymap

There are a number of zeropage locations used by JIFFYDOS (and
S-JIFFYDOS). These locations are also used by the JIFFYDOS kernal
built into RAMLINK and RAMDRIVE. It is best to avoid using theese
locations in Your own programs in order to retain complete JIFFYDOS
compatibility. At the very least, You should make sure that Your use of
them does not interfere with JIFFYDOS usage.

Location   Variable Name  Note

$26        ALLFLAG/RSIZE    2
     at filecopy:-0 = no REL file
                 -1-ff = REL file, contains then record length

$27        COMSAV           2
     which JIFFYDOS wedge comand

($55,$56      -             4
     location of jump (....) of the JIFFYDOS wedge comands
     at load: Load start adress)

($5f,$60      -             4
     vector on basic line at @d and @$)

$9b        KEYBYT           2
     00 function keys on
     ()00 function keys off

$9f        CJLA             2
     logical channel number for open
       $60 floppy directory
       $6e floppy file read/write
       $6f floppy comand/error-channel
       $7f printer
     (at floppy: logical channel number = secundary adress)

$a3        LDFLG/QFLAG      3
     bit 7  - usually: flag for end or identify
            - at load: flag for CBM- (0) or JD- (1) load
     bit 6  flag for CBM- (0) or JD- (1)- IEC bus routines
     bit 5  no funktion (after talk: 0, after listen: 1)
     bit 4-0  devicenumber of JD-floppy (not used)
     (! at C64-SJD bit 5-0 is used for the userport printer)

$a6        TFLAG            2
    at filecopy, @t und errorchannel: 0 = no REL file
                                      1-ff = REL file and recordlength
$b0,$b1    KEYPTR           2
     vector on text of function keys

$b0        SPRSAV           1
     at JD load: Interims storage for spriteregister
                 (JD IEC routines switch off sprites)

$b1        RASSAV           1
     at JD load: rasterline in which badlines begin (includes vertical

$b2        REGSAV           1
     at JD load: Bit 0-2 of dd00 (VIC-banc, pin M of userport)

$be        DRVBYT           2
     actual device

$bf        DEST             2
     at filecopy: devicenumber of destination device

Note 1  Saved, then restored by LOAD routine (no other usage).
Note 2  Used only from BASIC for JIFFYDOS wedge comands, device
        toggle and function keys.
Note 3  Used in all disk access and LOAD routines.
Note 4  Not mentioned by CMD. Only found from me by analysing.

Thanks to:
Arndt Dettke
Near Letter Quantity
Jochen Adler