diff --git a/libsrc/atari/dio_stc.s b/libsrc/atari/dio_stc.s
new file mode 100644
index 000000000..992eebe70
--- /dev/null
+++ b/libsrc/atari/dio_stc.s
@@ -0,0 +1,52 @@
+;
+; Christian Groessler, October 2000
+;
+; this file provides the _dio_snum_to_chs function
+;
+; on the Atari this function is a dummy, it returns
+; cylinder and head 0 and as sector the sectnum it got
+;
+; void __fastcall__ _dio_snum_to_chs(_sectnum_t sect_num,
+;				     unsigned int *cyl,
+;				     unsigned int *head,
+;				     unsigned int *sector);
+; _sectnum_t - 16bit
+;
+
+ 	.export		__dio_snum_to_chs
+	.include	"atari.inc"
+	.importzp	ptr1,ptr2
+	.import		popax
+
+.proc	__dio_snum_to_chs
+
+	sta	ptr1
+	stx	ptr1+1		; save pointer to sector #
+	jsr	popax		; get pointer to head
+	sta	ptr2
+	stx	ptr2+1
+	lda	#0
+	tay
+	sta	(ptr2),y	; set head number
+	iny
+	sta	(ptr2),y
+	jsr	popax		; get pointer to cyl
+	sta	ptr2
+	stx	ptr2+1
+	dey
+	tya
+	sta	(ptr2),y	; set cylinder number
+	iny
+	sta	(ptr2),y
+	jsr	popax		; get sector #
+
+	dey
+	sta	(ptr1),y
+	iny
+	txa
+	sta	(ptr1),y
+
+	rts
+
+.endproc
+