more IEC work - the turnaround seems to work now

c64/kernal/iec_pull_data_release_atn_clk.s

@@ -0,0 +1,15 @@
+
+iec_pull_data_release_atn_clk:
+
+	;; Released CLK = DATA considered valid; for extra robustness on non-emulated
+	;; hardware give some lines few more cycles to stabilize; see page 10 of
+	;; http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
+	
+	lda CI2PRA
+	ora #BIT_CI2PRA_DAT_OUT         ; pull
+	sta CI2PRA
+	and #$FF - BIT_CI2PRA_CLK_OUT   ; release
+	sta CI2PRA
+	and #$FF - BIT_CI2PRA_ATN_OUT   ; release
+	sta CI2PRA
+	rts