Hi
I'm working on RS485 MAX485 communication from esp32s3 idf to silicon labs zigbee keypad(contains MAX3483 chip).
Connections:
keypad(MAX3483 ) -> TTL - RS485 Module
A -> A
B -> B
3.3V -> VCC
GND -> GND

TTL - RS485 Module -> ESP32-S3
DI -> GPIO-4
DE -> GPIO-42
RE -> GPIO-2
RO -> GPIO-5

If I make RE, DE to low at TTL-MAX485 side, I was able to read response given from MAX3483 chip.
when I try to send data from TTL-MAX485 to MAX3483 side, data reception is not happening at keypad

#include <stdio.h>
#include <string.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "driver/uart.h"
#include "driver/gpio.h"
#include "esp_log.h"

#define TAG "RS485_APP"

#define UART_NUM UART_NUM_1        // Use UART1
#define TXD_PIN GPIO_NUM_4         // TX pin
#define RXD_PIN GPIO_NUM_5         // RX pin
#define BAUD_RATE 9600             // Baud rate
#define RS485_WRITE_PIN GPIO_NUM_42 // DE & RE pin (connected together)
#define RS485_READ_PIN GPIO_NUM_2 // DE & RE pin (connected together)

uint8_t rxBuff_from_device[254];

// Function declarations
void process_rs485_data(uint8_t *DeviceRxBuff, int len);

// UART initialization
// UART initialization
void init_uart() {
    uart_config_t uart_config = {
        .baud_rate = BAUD_RATE,
        .data_bits = UART_DATA_8_BITS,
        .parity = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE
    };

    uart_driver_install(UART_NUM, 256, 256, 0, NULL, 0);
    uart_param_config(UART_NUM, &uart_config);
    uart_set_pin(UART_NUM, TXD_PIN, RXD_PIN, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE);

    gpio_set_direction(RS485_WRITE_PIN, GPIO_MODE_OUTPUT);
    gpio_set_direction(RS485_READ_PIN, GPIO_MODE_OUTPUT);

    gpio_set_level(RS485_WRITE_PIN, 1); // Default to RX mode
    gpio_set_level(RS485_READ_PIN, 1);
    
}

// Receiving data task
void get_data_from_device(void *pvParameters) {
    while (1) {
        int len = uart_read_bytes(UART_NUM, rxBuff_from_device, sizeof(rxBuff_from_device), pdMS_TO_TICKS(70));

        if (len > 0) {
            printf("Raw Response and len %d: ", len);
            for (int k = 0; k < len; k++) {
                printf("%02X ", rxBuff_from_device[k]);
            }
            printf("\n");
        }
        
      //  vTaskDelay(pdMS_TO_TICKS(1)); // Small delay
    }
}

// Function to send RS485 data to devices
void send_rs485_to_device(uint8_t *data, size_t length) {
  //  gpio_set_level(RS485_ENABLE_PIN, 1);  // Enable TX mode
  //  vTaskDelay(50 / portTICK_PERIOD_MS);  // Ensure GPIO switch before sending

    uart_write_bytes(UART_NUM, (const char *)data, length);

    vTaskDelay(100 / portTICK_PERIOD_MS);  // Allow transmission to complete
   // gpio_set_level(RS485_ENABLE_PIN, 0);  // Switch back to RX mode

   //  vTaskDelay(50 / portTICK_PERIOD_MS);  // Allow some time before reading response
}


// // One-time task to send data
void periodic_send_task(void *pvParameters) {
    uint8_t buftx[] = {0x84, 0xBA, 0x20, 0xFF, 0xFE, 0x92, 0x5E, 0x5F, 0x04, 0x01, 0x00, 0xB3, 0x11};
while(1){
    ESP_LOGI(TAG, "Sending RS485 data once...");
    send_rs485_to_device(buftx, sizeof(buftx));

    // Optionally delay to allow UART to finish
    vTaskDelay(1000 / portTICK_PERIOD_MS);
}
    // Delete this task after sending
   // vTaskDelete(NULL);
}

void app_main(void) {
    init_uart();
    xTaskCreate(periodic_send_task, "periodic_send_task", 4096, NULL, 4, NULL);
   // xTaskCreate(get_data_from_device, "get_data_from_device", 4096, NULL, 6, NULL);
}

side.
Kindly check my configurations and let me know if any modifications required.

 

You don't appear to be changing the state of your RE/DE output signals correctly when trying to transmit. The following lines are commented out in your send_rs485_to_device function:

//  gpio_set_level(RS485_ENABLE_PIN, 1);  // Enable TX mode
//  vTaskDelay(50 / portTICK_PERIOD_MS);  // Ensure GPIO switch before sending
...
// gpio_set_level(RS485_ENABLE_PIN, 0);  // Switch back to RX mode
//  vTaskDelay(50 / portTICK_PERIOD_MS);  // Allow some time before reading response

Also, your code seems to imply that the DE and RE pins are tied together in hardware:

#define RS485_WRITE_PIN GPIO_NUM_42 // DE & RE pin (connected together)
#define RS485_READ_PIN GPIO_NUM_2 // DE & RE pin (connected together)

Therefore, you should not be driving both of these pins. If this is the case, you only need to control one signal. The other of these pins should be set to an input (and disabled or not used) instead of an output so that you don't have two drivers connected to one another.