THVD8000: Master-to-multislave 485 communication

Colin,

What's the distance of the communication? Where and how the termination are placed? Do you mean the master doesn't receive any signal from the down side if more than one slave is attached? You mentioned 'the upper computer will communicate properly after the chip is removed'. Which chip did you refer to? Have you ever checked the bus waveform before and after 'the chip is removed'?

Regards,

Hao

Hi Hao,

1.The distance is less than 0.8m in the laboratory.

2.When the slave program is verified separately. The program for the slave is: the slave is in the receiving state all the time and sends the data back after the slave receives the correct data. While welding on the THVD8000 chip, they sent the data to the slave using the upper computer, which should have sent the same data back, but the slave did not respond, and then they removed the THVD8000 chip, sent the data, and the slave would return normally. So they suspect there is no signal input between the A B ports, which causes a high level between TX and RX, which affects communication between the upper and slave MCUs. (This problem was discovered during the validation process, but does not affect the subsequent master slave communication, they would like to ask why this is the case) The connection diagram for the slave and the upper is as follows:

3.While multi-slave communication is taking place, it is not that the host is unable to receive the signal, but when communication is taking place, there is a problem at one node where the slave does not send a signal back to the host. The situation is as follows: The host program sends the data to the first slave, after the host gets the data back from the slave and determines that the data is correct, then sends the data to the next slave, so that it always circulates back to the seven slave, and if the data returned from the slave is wrong, the host gives the slave again, the host sends the same data, and if the host does not receive data back from the slave, the host remains in the receive state, stopping communication. So it can be judged that the communication was lost because one of the slaves did not send back data to the host. they want to know what the problem is.

Thanks,

Colin

Colin,

Thanks for your explanation, which helps me understand the system. However I'm still not sure how the data is sent to the slave without the THVD8000? Is the digital logic directly sent over the capacitor? I would also like to confirm if the point to point communication (one master and one slave) works fine. 

Regards,

Hao

Hi Hao,

1.As the picture shows, upper computer send the data to slave's MCU through USB2UART converter. Without the THVD8000, it works normal, but abnormal with THVD8000.

2.It works fine when point to point.

Best Regards,

Colin

Colin,

Is it possible to capture the waveforms like

1) point to point

2) point to point + THVD8000 slave

3) point to point + UART slave

You mentioned 60Ohm termination. How many termination on the bus? Does the slave node come with any termination?

Regards,

Hao

Hi Hao,

Maybe I didn't describe the issue clearly, there are two main issues currently:

1.Without THVD8000, upper computer can communicate with point's MCU normally through uart2usb converter. With THVD8000, upper computer send data to point's MCU but no data feedback.

2.One master and seven slaves with THVD8000: master send data to first slave and get feedback, then send data to next slave, until the last slave communication is completed. But one of the slave would have problem and don't feedback data to master, the entire communication will be stuck.

Best Regards,

Colin

Colin,

Thanks for your explanation. It would be nice to share the system schematic with me.  

1. Is it possible to capture the waveform of uart and thvd8000 communication?

2. Is it possible to capture the waveform of successful point-to-point and failed master-slave communication?

Regards,

Hao