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- For RS485 networks, pull-up and pull-down resistors are used to ensure a known logic state when the receiver is disconnected or the bus is open1. These resistors are not strictly required, but they help define the state of each pin on the RS-485 transceiver even when the MCU is powered down or disabled2. It is important to select the resistors such that the voltage between A and B is larger than 200mV when there is an open1. The RS-485 transceiver must be able to handle a common-mode load of 375 ohms3.Learn more:✕This summary was generated using AI based on multiple online sources. To view the original source information, use the "Learn more" links.
For parts that are not true fail-safe, RS485 network requires pull up (A) and pull down (B) resistors to guarantee that the receiver output is at a known logic state (logic high) when it is disconnected or the bus is open. Since receiver's differential threshold for logic high is 200mV (for components that are not true fail-safe), the pull-up, and pull-down resistors need to be selected such that...
ez.analog.com/interface-isolation/w/documents/232…The pull-up and pull-down resistors are not required. They are just used so that the state of each pin on the RS-485 transceiver is defined even when the MCU is powered-down, disabled, etc. If this is not a concern, you can simply connect the MCU outputs directly to the transceiver.e2e.ti.com/support/interface-group/interface/f/interf…Pull-up and pull-down resistors can be used on an RS-485 bus to accomplish fail-safe biasing, but this needs only to be done once at one node. You shouldn't need to place pull-up and pull-down resistors at each node. An RS-485 transceiver is required to handle a common-mode load of 375ohms.e2e.ti.com/support/interface-group/interface/f/interf… pullup - RS485 Pull-up, Pull-down and EOL resistors
The pull-up/-down resistors are often called "fail-safe resistors"; their purpose is to get a specific bus state even when no transmitter is active. You do not actually need them if all receivers have a built-in failsafe circuit (the LTC1685 has it), …
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Mar 11, 2020 · It depends on the cable and the existing config of the 680 ohms resistors. If you have pull ups and pull downs on each of the A and B wires then you are terminating in 170 ohms effectively and you might need between 220 …
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Sep 19, 2020 · In Datasheet, for transient protection against surge transients, it's recommended to use the circuit below: In this circuit, there is a pull-up resistor for 'receiver output' (R) pin, and also a pull-down resistor for 'driver enable' (DE) …
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Jun 22, 2016 · The pull-up and pull-down resistors are not required. They are just used so that the state of each pin on the RS-485 transceiver is defined even when the MCU is powered-down, disabled, etc. If this is not a concern, you can …
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