diff --git a/src/dos_m65/,aliases_dos.s b/src/dos_m65/,aliases_dos.s
index 3b6ec8de..3bf30ab4 100644
--- a/src/dos_m65/,aliases_dos.s
+++ b/src/dos_m65/,aliases_dos.s
@@ -66,15 +66,17 @@
 	!addr PAR_FNAME        = $8021 ; 16 bytes - filename, filled with $A0
 	!addr PAR_FPATTERN     = $8031 ; 16 bytes - pattern to match, filled with $A0
 
+	!addr PAR_FSINSTANCE   = $8041 ; 0 = SD card, 1/2 = floppy, 3 = ram disk
+
 	; Various temporary data
 
-	!addr XX_DIR_PHASE     = $8041 ; directory output phase, values deponds on device driver, but 0 = not reading
-	!addr SD_DIR_PHASE     = $8041 ; - SD card
-	!addr F0_DIR_PHASE     = $8042 ; - floppy 0
-	!addr F1_DIR_PHASE     = $8043 ; - floppy 0
-	!addr RD_DIR_PHASE     = $8044 ; - ram disk
+	!addr XX_DIR_PHASE     = $8042 ; directory output phase, values deponds on device driver, but 0 = not reading
+	!addr SD_DIR_PHASE     = $8042 ; - SD card
+	!addr F0_DIR_PHASE     = $8043 ; - floppy 0
+	!addr F1_DIR_PHASE     = $8044 ; - floppy 0
+	!addr RD_DIR_PHASE     = $8045 ; - ram disk
 
-	; Free space: $8045-$8063
+	; Free space: $8046-$8063
 
 	!addr SD_ACPTR_helper  = $8052 ; subroutine in RAM to read a byte
 	!addr code_LDA_01      = $8052 ; - LDA instruction
diff --git a/src/dos_m65/lowlevel/lowlevel_readsector.s b/src/dos_m65/lowlevel/lowlevel_readsector.s
index 7b7f1dbc..9af6dd94 100644
--- a/src/dos_m65/lowlevel/lowlevel_readsector.s
+++ b/src/dos_m65/lowlevel/lowlevel_readsector.s
@@ -2,6 +2,9 @@
 ; Read a sector pair from a block device
 
 
+; XXX utilize PAR_FSINSTANCE
+
+
 lowlevel_readsector:
 
 	; Set drive, ensure disk is present
diff --git a/src/dos_m65/pseudoiec/msg_acptr.s b/src/dos_m65/pseudoiec/msg_acptr.s
index 96b5934f..03ba153f 100644
--- a/src/dos_m65/pseudoiec/msg_acptr.s
+++ b/src/dos_m65/pseudoiec/msg_acptr.s
@@ -13,6 +13,10 @@ msg_ACPTR:
 	ldx IDX1_TALKER
 	+bmi msg_ACPTR_fail_no_talker
 
+	; Set file system instance
+
+	stx PAR_FSINSTANCE
+
 	; Check if active channel is status one
 
 	lda XX_CHANNEL, X
diff --git a/src/dos_m65/pseudoiec/msg_ciout.s b/src/dos_m65/pseudoiec/msg_ciout.s
index 369d38d3..29ce9597 100644
--- a/src/dos_m65/pseudoiec/msg_ciout.s
+++ b/src/dos_m65/pseudoiec/msg_ciout.s
@@ -13,8 +13,14 @@ msg_CIOUT:
 
 	ldx IDX1_LISTENER
 	bmi msg_CIOUT_fail
-	lda XX_MODE, x
 
+	; Set file system instance
+
+	stx PAR_FSINSTANCE
+
+	; Check current operation mode
+
+	lda XX_MODE, x
 	cmp #$01
 	bne @1
 
diff --git a/src/dos_m65/pseudoiec/msg_second.s b/src/dos_m65/pseudoiec/msg_second.s
index c0481254..cf9195ca 100644
--- a/src/dos_m65/pseudoiec/msg_second.s
+++ b/src/dos_m65/pseudoiec/msg_second.s
@@ -16,6 +16,7 @@ msg_SECOND:
 
 	ldx IDX1_LISTENER
 	bmi msg_SECOND_done        ; do nothing if no listener
+	stx PAR_FSINSTANCE         ; set file system instance
 	sta XX_CHANNEL, x          ; store channel
 
 	; Determine command type
diff --git a/src/dos_m65/unit_sdcard/unit_sd_cmd_open.s b/src/dos_m65/unit_sdcard/unit_sd_cmd_open.s
index 56a2629d..20cfc828 100644
--- a/src/dos_m65/unit_sdcard/unit_sd_cmd_open.s
+++ b/src/dos_m65/unit_sdcard/unit_sd_cmd_open.s
@@ -24,8 +24,6 @@ unit_sd_cmd_OPEN_EOI:
 	dey
 	bpl @lp1
 
-	; XXX add support for second card
-
 	lda SD_CMDFN_BUF
 	cmp #'$'
 	beq unit_sd_cmd_OPEN_dir