;;
;; Official Kernal routine, described in:
;;
;; - [RG64] C64 Programmer's Reference Guide   - page 303
;; - [CM64] Compute's Mapping the Commodore 64 - page 224
;; - https://www.pagetable.com/?p=1031, , https://github.com/mist64/cbmbus_doc
;; - http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
;;
;; CPU registers that has to be preserved (see [RG64]): .X, .Y
;;


unlsn:

	;; According to serial-bus.pdf (page 15) this routine flushes the IEC out buffer
	jsr iec_tx_flush

	;; Buffer empty, send the command
	lda #$3F

	jmp common_open_close_unlsn_second