ESP8266: How to set low logic level in RX?

I created a test circuit for RS485 communication with ESP8266 12E and SN75176 (RS485) chip and I noticed a problem in the voltage levels of the ESP8266. The ESP8266 RX pin is always HIGH when no communication is taking place (I have already tested with several NodeMCU ESP8266 12E boards). This logic level disrupts the SN75176’s operation, so I added the D6 diode as shown in the attached diagram (it works).

How do I make the ESP8266 RX always stay on the LOW logic level when communication is not occurring?

wBB: I created a test circuit for RS485 communication with ESP8266 12E and SN75176 (RS485) chip and I noticed a problem in the voltage levels of the ESP8266. The ESP8266 RX pin is always HIGH when no communication is taking place (I have already tested with several NodeMCU ESP8266 12E boards). This logic level disrupts the SN75176's operation, so I added the D6 diode as shown in the attached diagram (it works).

How do I make the ESP8266 RX always stay on the LOW logic level when communication is not occurring?

Looking at the SN75176 data sheet, the state of the RX pin should make no difference if the SN75176 Receive enable is high.

Paul

|500x353 While the TE pin is High (D8) the [u]RE/u Recieve is disabled, you should remove the diode or you can not receive on the port (unless you don't want to, but then you should not connect it at all but ground it out) Also the way you put the diode you actually put the RX pin of the MX485 HIGH not LOW, proving the point Paul is making, what are you connecting the MAX485 to ? common GND is required, and 120R accross as a terminator preferred.

Paul_KD7HB, D8 Pin of ESP8266 must be high logic level when I want to transmit data, that is, D8 = 1 means that RE and DE of SN75176 = 1 also. For the ESP8266 to receive data, then D8 must be low logic level (otherwise SN75176 will not send to ESP8266).

On the other hand, it really shouldn't make any difference the logic level of RX pin from ESP8266, but it's not what's happening. So I had to put the diode and that was the only way to make the circuit work.

For this reason I asked if there is a way to put the RX pin in logic low. Thanks!

Deva_Rishi, I'm not using the MAX485 chip, but the SN75176, which is different.

wBB: Deva_Rishi, I'm not using the MAX485 chip, but the SN75176, which is different.

They are fully interchangeable ! Just produced by a different Company. As i said before if you have the diode in that direction, the rx pin of the SN75176 is held by the rx of the ESP, which is what you are trying not to do.

the UART RX pin must be HIGH. the TX pin pulls it LOW to send pulses