SN65HVD1780: PU/PD resistor inquire

Hello Shu-Cheng,

Thank you for the question.  

You will be able to remove the R289 and R290 resistors and rely on the integrated fail-safe biasing in the SN65HVD1780 if each node in the network uses a receiver with fail-safe biasing capability.  

If one or more receivers on the bus do not have integrated fail-safe biasing, these external resistors will be required.  But if you are using SN65HVD1780 for each transceiver in the network, then you can safely remove the external resistors and rely on the fail-safe feature for protection at each node.  

Here is a blog post on the basics of RS-485 fail-safe biasing if you would like to read more about it.

Please let me know if you have any further inquiries.

Best Regards,

Max Megee