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SN65LBC184:About the chip communication signal conflict, information collection can not be the problem

Other Parts Discussed in Thread: SN65LBC184

零件编号:SN65LBC184

工具/软件:

 逆变器的ARM芯片通过485芯片连接到总线,集电极通过485通信连接到总线。

 此时,ARM 会发送一个软重置信号。在 reset 期间,collector 发送一个信号,并且这两个信号重合。当使用串口助手在总线上采集数据时,此时无法采集数据,没有乱码数据。

我们想知道为什么我们无法捕获总线上的数据。

 这是连接到 485 芯片的 ARM 芯片的原理图。

 通道 3 是 reset 信号,电压探针夹住 485 芯片的引脚 6 和 7。通道 4 使用电压探针钳制 485 芯片的引脚 2 和 5

 通道 3 是 reset 信号,电压探针夹住 485 芯片的引脚 6 和 7。通道 4 使用电压探针钳制 485 芯片的引脚 1 和 4

  • The schematic shows a pull-down resistor to −5 V. Is this correct? The device does not support logic voltages below GND.

    Are you using an isolated voltage probe? If not, then the probe is shorting one of the bus lines to ground, which will garble the signal. To measure an RS-485 signal, use two channels to measure A and B relative to GND, and tell the oscilloscope to compute A − B.

  • Hi Wneqi,

    As Clemens pointed out the -5V on the pins shouldn't be present since it's outside of the absolute max for the device. 

    I'm also confused as to what the scopeshots are showing. What is ch3 and ch4? 

    More specifically, Can you put a probe on the D pin, A pin, and B pin? We should monitor the transmission of whatever data you're sending to see if it makes it through the transceiver and onto the cables. 

    -Bobby

  • The schematic error has now been fixed.I used an isolated voltage probe.

  • As far as I can see, these waveforms show that the SN65LBC184 correctly transmits the reset signal to the bus.

    Why have you shown these waveforms? What exactly is unexpected about them?

  • I wanted to prove why we couldn't capture the data on the bus when the chip was intact.Focus on the yellow text.

  • The oscilloscope signals show only the reset signal on the bus.

    If the collector's data does not appear on the bus, then this looks like a problem with the collerctor's transceiver. Please show an oscilloscope trace of the TX, DE, and A − B signals of that transceiver.

  • Hi Wneqi,

    As Clemens mentioned, please collect the requested scopeshot images. For the A-B pins you should collect them at the receiver side of the cable (not the transmission side).

    -Bobby