通过串口发送出AT，缺返回不了OK，求解
求解求解答55555555555555555555
1，串口硬件连接错误，或者波特率错误
2，你用的ESP8266并不是烧写了AT固件的
GPIO2 (TX) 连接串口的 RX，观察 是否有 Log 输出，正常能观察到 ESP8266 的启动信息。...
boot: ESP-IDF v3.4-rc 2nd stage bootloader
I (54) boot: compile time 11:18:21
I (54) boot: SPI Speed : 80MHz
I (57) boot: SPI Mode : DIO
I (61) boot: SPI Flash Size : 2MB
I (65) boot: Partition Table:
I (68) boot: ## Label Usage Type ST Offset Length
I (75) boot: 0 otadata OTA data 01 00 00009000 00002000
I (83) boot: 1 phy_init RF data 01 01 0000f000 00001000
I (90) boot: 2 ota_0 OTA app 00 10 00010000 000e0000
I (98) boot: 3 at_customize unknown 40 00 000f0000 00020000
I (105) boot: 4 ota_1 OTA app 00 11 00110000 000e0000
I (112) boot: 5 nvs WiFi data 01 02 001f0000 00010000
I (120) boot: End of partition table
I (124) boot: No factory image, trying OTA 0
I (129) esp_image: segment 0: paddr=0x00010010 vaddr=0x40210010 size=0xac0d0 (704720) map
I (138) esp_image: segment 1: paddr=0x000bc0e8 vaddr=0x402bc0e0 size=0x1aba8 (109480) map
I (146) esp_image: segment 2: paddr=0x000d6c98 vaddr=0x3ffe8000 size=0x00788 ( 1928) load
I (155) esp_image: segment 3: paddr=0x000d7428 vaddr=0x40100000 size=0x00080 ( 128) load
I (164) esp_image: segment 4: paddr=0x000d74b0 vaddr=0x40100080 size=0x059c4 ( 22980) load
I (173) boot: Loaded app from partition at offset 0x10000
phy_version: 1163.0, 665d56c, Jun 24 2020, 10:00:08, RTOS new
max tx power=78,ret=0
2.0.0
RX 接回 GPIO15 (TX)， 发送 AT 命令，注意 AT 命令结尾应为 ASCII 字符的 \r\n