diff --git a/apps/basic/README.md b/apps/basic/README.md
index 417a46f..50144e0 100644
--- a/apps/basic/README.md
+++ b/apps/basic/README.md
@@ -238,3 +238,10 @@ contents. Any line not starting with a number is ignored (not an error).
 is iterated to see if it finds a file with the same name. If it does, it loads
 its contents at `USER_CODE` (from `user.h`) and calls that address, with HL
 pointing to the the remaining args in the command line.
+
+The user code called this way follows the *usr* convention for output, that is,
+it converts all registers at the end of the call and stores them in appropriate
+variables. If `A` is nonzero, an error is considered to have occurred.
+
+It doesn't do var-to-register transfers on input, however. Only HL is passed
+through (with the contents of the command line).
diff --git a/apps/basic/fs.asm b/apps/basic/fs.asm
index d097582..1f9502c 100644
--- a/apps/basic/fs.asm
+++ b/apps/basic/fs.asm
@@ -86,7 +86,6 @@ basFNEW:
 	call	rdSep		; HL now points to filename
 	push	ix \ pop de
 	ld	a, e
-	out	(42), a
 	jp	fsAlloc
 
 ; Deletes filename with specified name
@@ -114,11 +113,18 @@ basPgmHook:
 	inc	hl		; Z preserved in 16-bit
 	inc	de		; Z preserved in 16-bit
 	jr	z, .loop
-	; Ready to jump. Return USER_CODE in IX and basCallCmd will take care
-	; of setting (HL) to the arg string.
-	ld	ix, USER_CODE
+	; Ready to jump. Return .call in IX and basCallCmd will take care
+	; of setting (HL) to the arg string. .call then takes care of wrapping
+	; the USER_CODE call.
+	ld	ix, .call
 	cp	a		; ensure Z
 	ret
+.call:
+	ld	iy, USER_CODE
+	call	callIY
+	call	basR2Var
+	or	a		; Z set only if A is zero
+	ret
 
 basFSCmds:
 	.dw	basFLS
diff --git a/apps/basic/main.asm b/apps/basic/main.asm
index 09d1771..8014b44 100644
--- a/apps/basic/main.asm
+++ b/apps/basic/main.asm
@@ -415,6 +415,7 @@ basUSR:
 	; and finally, A
 	ld	a, (VAR_TBL)
 	call	callIY
+basR2Var:	; Just send reg to vars. Used in basPgmHook
 	; Same dance, opposite way
 	ld	(VAR_TBL), a
 	ld	(VAR_TBL+46), ix