About RS485 communication receiving and sending control

stm32f103vct6

About RS485 communication receiving and sending control [Copy link]

The transmit and receive pins of the 485 chip can be pulled down to the ground with only a 10K resistor. When sending, the ST microcontroller outputs a high level 1, and when receiving, the pin outputs a low level 0. Why do many people need to add a triode switch circuit to control the transmit and receive pins when designing 485 circuits? It feels redundant, unless you do isolation, and isolation is also done with optocouplers.

dcexpert

The transistor is added to control RE with the sending signal TXD, in order to save one IO.

damiaa

It doesn't matter what you do. As long as the logic is correct, the timing, voltage, current, and conditions are met, it's fine. Whatever you want is fine.

Verifone

damiaa posted on 2024-4-30 08:45 It doesn't matter what you do. As long as the logical relationship is correct, the timing, voltage, current, and conditions are met, it's fine. Whatever you want is fine.

You are right, just make sure it meets your needs. All the settings are for better operation. The applicable environments are different.

chunyang

Of course, no transistor is needed to control the switching of transmission and reception separately, but what if there is not enough IO to control it? The 485 interface circuit with transistor control of transmission and reception mentioned by the OP is the so-called "automatic switching" circuit. What is the principle? The OP may wish to understand it yourself and then explain why it is designed this way.

beyond_笑谈

If the control system is relatively simple, it is OK to use the pins of the microcontroller to directly control it. However, if the controller circuit is complex, it is better to add a first-level driver. For example, in an industrial control board, a trigger is added after the CPU pin comes out for driving.