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SN65HVD1782: About the selection of pull-up and pull-down resistors on the AB bus of the 485 converter chip

SHENG YANG

Expert 1320 points

Part Number: SN65HVD1782

HI ALL!

The current design uses the 485 interface chip SN65HVD1782, as shown in the above figure A, B bus pull-up and pull-down resistor value selection should be how to choose.Does TI have a specific manual to explain this? If so, please provide it. Thank you.

over 2 years ago

0 SHENG YANG over 2 years ago

Expert 1320 points

SN65HVD1782 can only be used in half-duplex mode and cannot be used in full-duplex mode, is this understanding correct?

+1 Clemens Ladisch over 2 years ago

Guru 316690 points

The SN65HVD1782 has a failsafe receiver and does not need failsafe biasing.

If there are other receivers without integrated failsafe on the bus, then the bus does need failsafe biasing. See the blog RS-485 basics: two ways to fail-safe bias your network and application notes like RS-485 failsafe biasing: Old versus new transceivers, RS-485: Passive failsafe for an idle bus - Texas Instruments, AN-847 FAILSAFE Biasing of Differential Buses, AN-1057 Ten Ways to Bulletproof RS-485 Interfaces, and Failsafe in RS-485 data buses.

A full-duplex transceiver would have separate A/B and X/Y pins.

0 SHENG YANG over 2 years ago in reply to Clemens Ladisch

Expert 1320 points

Thank you very much!