Because you need both a voltage source and a ground in order to create a complete circuit, you need to have a sourcing input or output connected to a sinking output or input.
因为在一个完整的电路中必须有一对电源和地。
2
The sinking digital output controls the line by using a transistor to leave the line high (at + v) or to ground the line to 0 v.
Sinking数字输出通过三极管来控制连接线上的电平为高电平(+ V)或是低电平(0 V)。
3
Since the 20th century, when Wells began to draw water from the groundto support local industry, Venice has been sinking.