THVD1552: Double Termination resistor for full-duplex

Hi Honda,

thanks for reaching out on E2E and thanks for posting the pictures because this way it's easier for me to understand your problem.

The two devices that you are showing are similar in fact they are both RS485 full duplex transceivers but the applications that you show in those two pictures are different. Specifically the THVD1552 presented here is used in a Multi-Point configuration and the bus is shared among many slave units. In this configuration you need to terminated both ends of each line since when a slave is talking on the bus the signal can create reflection on both sides of the lines, thus terminations.

On the other hand, the other device shown in your pictures is used in a Point-to-Point configuration; this configuration only needs one termination per line since there is only one driver communicating to one receiver.

For your information, TI has many application notes were we try to give an overview for some standards. If you're interested in RS485 you can read the following material which explains quite well the RS485 Standard and the different configurations possible:

Please let me know if this helps you or if you have any other question.

Best regards,

Adrian