MAX3485/MAX485 Low-Power Shutdown Mode

Question

I am using a MAX3485 for Modbus communication through UART between a device and a Modbus server. What I want to achieve is to put my MAX3485 breakout into low-power shutdown mode when I put my device into deep sleep 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 server that is powered by the 5V/GND of my device

From the MAX3485 datasheet, 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 2 nA 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)?

Answer 1

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.