diff --git a/Firmware/src/AppleIISd.inc b/Firmware/src/AppleIISd.inc
index 5659e3e..ff55100 100644
--- a/Firmware/src/AppleIISd.inc
+++ b/Firmware/src/AppleIISd.inc
@@ -1,10 +1,10 @@
 ;*******************************
 ;
 ; Apple][Sd Firmware
-; Version 1.2
+; Version 1.3
 ; Defines
 ;
-; (c) Florian Reitz, 2017 - 2018
+; (c) Florian Reitz, 2017 - 2019
 ;
 ; X register usually contains SLOT16
 ; Y register is used for counting or SLOT
@@ -61,7 +61,7 @@ WP          =     $20
 CD          =     $40
 INITED      =     $80
 
-SMDRIVERVER =     $120B       ; Version 1.2 Beta
+SMDRIVERVER =     $130B       ; Version 1.3 Beta
 
 ; Error codes
 NO_ERR          =     $00
diff --git a/Firmware/src/AppleIISd.s b/Firmware/src/AppleIISd.s
index 7e17e4a..c13f25d 100644
--- a/Firmware/src/AppleIISd.s
+++ b/Firmware/src/AppleIISd.s
@@ -1,10 +1,10 @@
 ;*******************************
 ;
 ; Apple][Sd Firmware
-; Version 1.2.1
+; Version 1.3
 ; Main source
 ;
-; (c) Florian Reitz, 2017 - 2018
+; (c) Florian Reitz, 2017 - 2019
 ;
 ; X register usually contains SLOT16
 ; Y register is used for counting or SLOT
@@ -368,7 +368,7 @@ INIT:       LDA   #$03        ; set SPI mode 3
             RTS
 
 
-TEXT:       .asciiz " Apple][Sd v1.2.1 (c)2018 Florian Reitz "
+TEXT:       .asciiz " Apple][Sd v1.3 (c)2019 Florian Reitz "
 
 CMD0:       .byt $40, $00, $00
             .byt $00, $00, $95
diff --git a/Firmware/src/Helper.s b/Firmware/src/Helper.s
index 0f659e2..3eeca24 100644
--- a/Firmware/src/Helper.s
+++ b/Firmware/src/Helper.s
@@ -1,10 +1,10 @@
 ;*******************************
 ;
 ; Apple][Sd Firmware
-; Version 1.2
+; Version 1.3
 ; Helper functions
 ;
-; (c) Florian Reitz, 2017 - 2018
+; (c) Florian Reitz, 2017 - 2019
 ;
 ; X register usually contains SLOT16
 ; Y register is used for counting or SLOT
@@ -102,10 +102,13 @@ GETR3:      JSR   GETR1       ; get R1 first
 ;*******************************
 ;
 ; Calculate block address
-; Unit number is in $43 DSSS0000
+; Unit number is in $43 DSSS0000 / DSSS00DD
 ; Block no is in $46-47
 ; Address is in R30-R33
 ;
+; Starting ProDOS 2.5a5 the unit number
+; has been enhanced to DSSS00DD
+;
 ;*******************************
 
 GETBLOCK:   PHX               ; save X
@@ -116,21 +119,35 @@ GETBLOCK:   PHX               ; save X
             STA   R33,X       ; in R30-R33
             LDA   BLOCKNUM+1
             STA   R32,X
-            STZ   R31,X
             STZ   R30,X
 
-            TYA               ; get SLOT16
+.if 1
+            LDA   DSNUMBER    ; calculate drive number
+            ASL   A
+            AND   #$07
+            ADC   #$01
+            STA   R31,X
+.else
+            LDA   DSNUMBER
+            AND   #$03        ; mask extended drive bits (bits 0-1)
+            STA   R31,X
+            BIT   DSNUMBER    ; check old drive number (bit 7)
+            BPL   @PHANTOM
+            INC   A           ; increase by one
+            STA   R31,X
+.endif
+.if 0
+@PHANTOM:   TYA               ; get SLOT16
             EOR   DSNUMBER
             AND   #$70        ; check only slot bits
-            BEQ   @DRIVE      ; it is our slot
-            LDA   #2          ; it is a phantom slot
-            STA   R31,X
-
-@DRIVE:     BIT   DSNUMBER    ; drive number
-            BPL   @SDHC       ; D1
-            LDA   R31,X       ; D2
-            INC   A
+            BEQ   @SDHC       ; it is our slot
+            LDA   R31,X       ; it is a phantom slot, multiply by 16
+            ASL   A
+            ASL   A
+            ASL   A
+            ASL   A
             STA   R31,X
+.endif
 
 @SDHC:      LDA   #SDHC
             AND   SS,Y        ; if card is SDHC,
@@ -144,7 +161,7 @@ GETBLOCK:   PHX               ; save X
             DEY
             BNE   @LOOP
   
- @END:      PLY               ; restore Y
+@END:       PLY               ; restore Y
             PLX               ; restore X
             RTS