The bus is "idle" when both lines are high (open-collector).
总线空闲时，两条线都是高电平(集电极开路)。
2
If another voltage or current source is present, you could replace S1 with an open-collector switch that sinks current only.
如果另外有个电压或电流源存在，用仅有减小电流作用的集电极开路开关代替s1。
3
To commemorate the occasion, Australian Open organisers have struck a special limited edition collector coin that was released at the Australian Open 2012 launch this morning.