Electrical – MAX3485/MAX485 Low-Power Shutdown Mode

low-powerrs485

I am using a MAX3485 for modbus communication through UART between a device and a modbus slave.
What I want to achieve is to put my MAX3485 breakout into low-power shutdown mode when I put my device into deepsleep mode.

The wiring my MAX3485 breakout is as followed:

  • DI/RO => UART GPIO of my device
  • RE/DE => 2 distinct GPIO of my device
  • Vcc/Gnd => respectively 3.3V/GND of my device
  • A/B => to the A/B of my modbus slave that is powered by the 5V/GND of my device

From the MAX3485 dataeet, I can read:

Low-Power Shutdown Mode (MAX3483/MAX3485/MAX3486/MAX3491)
A low-power shutdown mode is initiated by bringing both RE high and DE low. The devices will not shut down unless both the driver and receiver are disabled (high impedance). In shutdown, the devices typically draw only 2nA of supply current.

Bringing RE high and DE low is not an issue but how to achieve: the driver and receiver are disabled (high impedance). ?

Thank you in advance,

Bnjroos

Best Answer

Just bring RE high and DE low. From the datasheet:

RO is enabled when RE is low; RO is high impedance when RE is high.

and

The driver outputs are enabled by bringing DE high. They are high impedance when DE is low.

So when RE is driven high and DE is driven low simultaneously the receiver and transmitter will be in high impedance state.

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