Urgent!!! Please help me, is there any problem with the design of the serial port chip max3485esa? Why can't I echo the data?

rzp

jobszheng5

Our design at the time was similar to yours, except that we didn't add resistors and LED lights to the TTL.

You can try to remove the above devices first, then pull the control pin low to enter the receiving mode and see if there is any level coming from the TTL side?

rzp

jobszheng5 posted on 2024-9-2 18:02 Our design at that time was similar to yours, except that we did not add resistors and LED lights to the TTL. You can try to remove the above components first, and then...

Just remove these two resistors?

beyond_笑谈

rzp posted on 2024-9-2 20:10 Just remove these two resistors?

The circuit diagram is too blurry to see clearly. The resistors of RX and TX will not affect communication.

rzp

beyond_笑谈Published on 2024-9-2 21:16 The circuit diagram is too blurry to see clearly. The resistors of RX and TX will not affect communication

Is this clearer?

damiaa

rzp posted on 2024-9-2 21:26 Is this clearer?

Try removing the resistors in the TX and RX strings and short-circuiting them. In addition, PC4 controls the transmission and reception, so it transmits when it is high and receives when it is low.

chunyang

If both the MCU and 485 interface are powered by 3V, R41 and R43 are unnecessary and should be removed. The terminal resistor should only be configured at both ends of the bus, and the bias resistor should be calculated based on whether it is a single-point bias or a per-point bias.

As for "the echo data cannot be displayed", we should first analyze whether it is a software problem or a hardware problem. The specific judgment can be made with the help of PC serial port and serial port debugging software.

beyond_笑谈

You can try changing the resistors in series between RX and TX to 0R as suggested by the above people, but software checking is more necessary.

rzp

chunyang posted on 2024-9-2 23:09 If both the MCU and 485 interface are powered by 3V, R41 and R43 are unnecessary and should be removed. The terminal resistor should only be configured at both ends of the bus, and the bias resistor needs to be based on...

Before power on, the measured values of A were 2.2V and B were -1.8V. After power on, they became 3.86 and -0.86.

rzp

chunyang posted on 2024-9-2 23:09 If both the MCU and 485 interface are powered by 3V, R41 and R43 are unnecessary and should be removed. The terminal resistor should only be configured at both ends of the bus, and the bias resistor needs to be based on...

Before power on, the measured voltages of A and B were 2.2V and -1.8V, but after power on, they became 3.86 and -0.86, respectively. This is the voltage measured by A and B of 485. What is the reason?

dukedz

For a circuit, echoing data means receiving the data it sends.

Your circuit obviously does not support echo

Your circuit has only two states: sending or receiving, and does not support sending + receiving at the same time

To support echo (send + receive at the same time), just connect pin 2 RE# directly to GND (receive is always enabled)

For hardware that does not support echo data, the host computer software can display the sent data to the window, so it has nothing to do with the hardware.

rzp

dukedz posted on 2024-9-3 10:04 For a circuit, echoing data means receiving the data it sends. Your circuit obviously does not support echoing. Your circuit has only two states: sending...

I pulled the pc4 up and down in the software to receive it, but pinrtf can't be displayed.

sky999

Remove the 120R resistor