sn65hvd1050芯片S管脚使能的问题

我用MCU控制sn65hvd1050的S管脚，如果首先给S管脚一个高电平，禁止其发送，确实发送停止了，过一段时间，再给S管脚一个低电平，按照PDF说明，感觉应该使能芯片了，会有输出，但是实际情况是仍然没有输出，仍然处于禁止的状态，只有重新上电以后，才可以再次进入使能状态，这是为什么？是芯片自身的设计么？怎么才能做到禁止后仍然可以再次使能？

应该就是通过高低电平来切换两种模式的啊。  有没有实测下S脚的电平变化？

Pin 8 provides for two different modes of operation: high-speed or silent mode. The high-speed mode of
operation is selected by connecting S (pin 8) to ground.
If a high logic level is applied to the S pin of the SN65HVD1050, the device enters a listen-only silent mode
during which the driver is switched off while the receiver remains fully functional.
In silent mode, all bus activity is passed by the receiver output to the local protocol controller. When data
transmission is required, the local protocol controller reverses this low-current silent mode by placing a logic-low
on the S pin to resume full operation.

现象确实很奇怪，CAN总线上挂了几个HVD1050?另外，是否有端接120ohm终端匹配电阻？