documentation update, added STATUS.md document

c64/kernal/second.s

@@ -1,8 +1,19 @@
-; Function defined on pp272-273 of C64 Programmers Reference Guide
+
+;;
+;; Official Kernal routine, described in:
+;;
+;; - [RG64] C64 Programmer's Reference Guide   - page 296
+;; - [CM64] Compute's Mapping the Commodore 64 - page 223/224
+;;
+;; CPU registers that has to be preserved (see [RG64]): .X, .Y
+;;
+
+;; XXX currently does not preserve registers, to be fixed!
+
 second:
 
-	;; This trivial routine is documented in 'C64 Programmer's Reference Guide', page 296 and
-	;; https://www.pagetable.com/?p=1031, , https://github.com/mist64/cbmbus_doc
+	;; see also https://www.pagetable.com/?p=1031, , https://github.com/mist64/cbmbus_doc
+
 	and #$1F ; make sure bits encoding the command are cleared out
 	ora #$60
 	jmp iec_tx_command