diff --git a/src/dos_m65/,aliases_dos.s b/src/dos_m65/,aliases_dos.s
index 031df0f1..96b2f5c2 100644
--- a/src/dos_m65/,aliases_dos.s
+++ b/src/dos_m65/,aliases_dos.s
@@ -7,19 +7,19 @@
 ; - additional 16KB RAM is reserved for DOS too ($14000-$17FFF), and can be banked-in if needed
 
 
-
 	;
-	; Page 0
+	; Page start+0
 	;
 
 	!addr MAGICSTR         = $8000 ; magic string; if not matching, DOS considered non-functional
 
 	; General DOS configuration
 
-	!addr UNIT_SDCARD      = $8005
-	!addr UNIT_FLOPPY      = $8006
-	!addr UNIT_RAMDISK     = $8007
+	!addr UNIT_SDCARD      = $8005 ; unit number for device, 0 = none
+	!addr UNIT_FLOPPY      = $8006 ; as above
+	!addr UNIT_RAMDISK     = $8007 ; as above
 
 	; General DOS status
 
-	!addr UNIT_HANDLER     = $8008
+	!addr IDX_LISTENER     = $8008 ; listener idx * 2, >=$80 = none
+	!addr IDX_TALKER       = $8009 ; talker   idx * 2, >=$80 = none
diff --git a/src/dos_m65/dos_init.s b/src/dos_m65/dos_init.s
index 8ef2e514..2b537af7 100644
--- a/src/dos_m65/dos_init.s
+++ b/src/dos_m65/dos_init.s
@@ -31,4 +31,10 @@ dos_INIT:
 	lda #CONFIG_UNIT_RAMDISK
 	sta UNIT_RAMDISK
 
+	; Clear listener / talker
+
+	lda #$FF
+	sta IDX_LISTENER
+	sta IDX_TALKER
+
 	rts
diff --git a/src/dos_m65/dos_listen_unlsn.s b/src/dos_m65/dos_listen_unlsn.s
new file mode 100644
index 00000000..e3bf5700
--- /dev/null
+++ b/src/dos_m65/dos_listen_unlsn.s
@@ -0,0 +1,99 @@
+
+;
+; Implementation of LISTEN/UNLSN/TALK/UNTLK commands.
+; For detailed description see 'm65dos_bridge.s' file.
+;
+
+
+; LISTEN
+
+dos_LISTEN:
+
+	pha
+	and #$1F
+	beq dos_fail_TALK_LISTEN           ; branch if device 0 (used to denote lack of device)
+
+	cmp UNIT_SDCARD
+	bne @1
+
+	lda #$00
+	bra dos_LISTEN_success
+@1:
+	cmp UNIT_FLOPPY
+	bne @2
+
+	lda #$02
+	bra dos_LISTEN_success
+@2:
+	cmp UNIT_RAMDISK
+	bne dos_fail_TALK_LISTEN
+
+	lda #$04
+	
+	; FALLTROUGH
+
+dos_LISTEN_success:
+
+	sta IDX_LISTENER
+	bra dos_common_LSN_TALK_UN
+
+; TALK
+
+dos_TALK:
+
+	pha
+	and #$1F
+	beq dos_fail_TALK_LISTEN           ; branch if device 0 (used to denote lack of device)
+
+	cmp UNIT_SDCARD
+	bne @1
+
+	lda #$00
+	bra dos_TALK_success
+@1:
+	cmp UNIT_FLOPPY
+	bne @2
+
+	lda #$02
+	bra dos_TALK_success
+@2:
+	cmp UNIT_RAMDISK
+	bne dos_fail_TALK_LISTEN
+
+	lda #$04
+	
+	; FALLTROUGH
+
+dos_TALK_success:
+
+	sta IDX_TALKER
+	bra dos_common_LSN_TALK_UN
+
+dos_fail_TALK_LISTEN:
+
+	pla
+	sec
+	rts
+
+; UNLSN / UNTLK
+
+dos_UNLSN:
+
+	pha
+	lda #$FF
+	sta IDX_LISTENER
+	bra dos_common_LSN_TALK_UN
+
+dos_UNTLK:
+
+	pha
+	lda #$FF
+	sta IDX_TALKER
+
+	; FALLTROUGH
+
+dos_common_LSN_TALK_UN:
+
+	pla
+	clc
+	rts
diff --git a/src/dos_m65/dos_unitset.s b/src/dos_m65/dos_unitset.s
index 49133f6d..9ef2326b 100644
--- a/src/dos_m65/dos_unitset.s
+++ b/src/dos_m65/dos_unitset.s
@@ -12,6 +12,8 @@ dos_UNITSET:
 	bcc @1
 	rts
 @1:
+	; XXX do not allow illegal device numbers... above 30 or below 8 ?
+
 	; Check what kind of device was requested
 
 	cmp #$00
diff --git a/src/dos_m65/stubs.s b/src/dos_m65/stubs.s
index 17c67de7..2c8a2052 100644
--- a/src/dos_m65/stubs.s
+++ b/src/dos_m65/stubs.s
@@ -5,18 +5,12 @@ dos_ACPTR:
 	+nop
 dos_CIOUT:
 	+nop
-dos_LISTEN:
-	+nop
 dos_SECOND:
 	+nop
-dos_TALK:
-	+nop
 dos_TKSA:
 	+nop
-dos_UNTLK:
-	+nop
-dos_UNLSN:
-	+nop
 
 	sec
 	rts
+
+