implemented MERGE command

c64/basic/engine/fetch_device_secondary.s

@@ -11,15 +11,9 @@ fetch_device_secondary:
 
 	// Fetch the device number
 
-	jsr injest_comma
-	bcs fetch_secondary
+	jsr fetch_device_secondary_uint8
+	bcs fetch_device_secondary_done
 
-	jsr injest_spaces
-	jsr basic_parse_line_number
-	lda LINNUM+1
-	bne_16 do_ILLEGAL_QUANTITY_error
-
-	lda LINNUM+0
 	sta FA
 
 	// FALLTROUGH
@@ -28,15 +22,9 @@ fetch_secondary:
 
 	// Fetch secondary address
 
-	jsr injest_comma
+	jsr fetch_device_secondary_uint8
 	bcs fetch_device_secondary_done
 
-	jsr injest_spaces
-	jsr basic_parse_line_number
-	lda LINNUM+1
-	bne_16 do_ILLEGAL_QUANTITY_error
-
-	lda LINNUM+0
 	sta SA
 
 	// FALLTROUGH
@@ -44,3 +32,18 @@ fetch_secondary:
 fetch_device_secondary_done:
 
 	rts
+
+
+fetch_device_secondary_uint8: // also called by 'cmd_merge'
+
+	jsr injest_comma
+	bcs !+
+
+	jsr injest_spaces
+	jsr basic_parse_line_number
+	lda LINNUM+1
+	bne_16 do_ILLEGAL_QUANTITY_error
+	lda LINNUM+0
+	clc
+!:	
+	rts