several IEC routines now properly preserve X/Y registers

c64/kernal/talk.s

@@ -4,18 +4,17 @@
 ;;
 ;; - [RG64] C64 Programmer's Reference Guide   - page 301/302
 ;; - [CM64] Compute's Mapping the Commodore 64 - page 223
+;; - https://www.pagetable.com/?p=1031, https://github.com/mist64/cbmbus_doc
 ;;
 ;; CPU registers that has to be preserved (see [RG64]): .X, .Y
 ;;
 
-;; XXX currently does not preserve registers, to be fixed!
+
 ;; XXX shouldn't this do a turnaround?
 
 talk:
 
-	;; 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 #$40
+	sta BSOUR
 	jmp iec_tx_command
-