THVD1406: How to configure if use auto-direction mode?

Zoe,

The device powers up with auto-direction mode enabled (can't be turned off). You don't need to do anything to enable it.

For the #SHDN pin, it basically controls the driver, if the pin is a logic low then A/B do not output anything (they are high-z)

#RE for a auto-directional device like THVD1406 will only temporary disable the receivers, after the tdevice_autodir time has expired it will re-enable it.

"When RE is logic high or left open and D input switches from logic low to logic high, the receiver output is high-impedance for the duration of tdevice-auto-dir. After the duration of tdevice-auto-dir, the receiver turns ON and outputs a logic high or low depending upon the differntial bus input voltage. "

So basically if you are trying to drive a signal from the D pin to the RS485 lines, you should enable by drivers by tying #SHDN to a logic high. If you are not trying to drive a signal and only want to receive, then you can tie #SHDN low.

-Bobby