Enabling RS485 UART driver and receiver at the same time

Question

I am a software engineer so I hope that my question not stupid:

I work on board with an half-duplex RS485 transceiver.

From the software, I can handle a GPIO to handle the output driver of the transceiver. But, the enable pin of the input receiver is tied at 0 on the board meaning that the receiver is always active. So when I sent data, the driver and the receiver are active at the same time.

I am afraid that the transceiver won't support this for long before burning.

The transceiver is a ADM4851ARZ and here is it's datasheet.

The only relevant thing I found is:

Half-duplex operation implies that the transceiver can transmit and receive, but it can do only one of these at any given time

So I have a bad feeling about that...

Could someone tell me if this is safe? Thanks!

Answer 1

You have receive \$\bar{RE}\$ enable and transmit enable \$DE\$, if both pins are together, then you will notice that they are negated, so when asserting RTS it will switch off the receiver and turn transmitter, when RTS is off then it switches back to recieve and turns off transmitter. Anyway if receive enable is constantly active, you will just recive what you send, echo. This won't hurt the UART of your MCU, you have just to disable receiving in software if you don't want the echo.

Answer 2

It won't damage anything. The receiver will just indicate the same symbol that's being transmitted (as long as the bus isn't shorted or contended).

Answer 3

The data sheet in the very first paragraph says quite explicitly...

...suitable for high speed, half-duplex and full duplex data communication on multipoint bus transmission lines.

Nothing appears to be in danger of "burning".