Understanding the ESP8266

Question

I've received my ESP8266-01 and playing with it I discovered that with a baudrate of 74880 I can get the boot modes and `hy version, etc: ets Jan 8 2013,rst cause:1, boot mode:(3,0)

load 0x40100000, len 1856, room 16 
tail 0
chksum 0x63
load 0x3ffe8000, len 776, room 8 
tail 0
chksum 0x02
load 0x3ffe8310, len 552, room 8 
tail 0
chksum 0x79
csum 0x79
2nd boot version : 1.5
 SPI Speed : 40MHz
 SPI Mode : DIO
 SPI Flash Size & Map: 8Mbit(512KB+512KB)
jump to run user1 @ 1000
rf cal sector: 249
rf[112] : 00
rf[113] : 00
rf[114] : 01
SDK ver: 1.5.4.1(39cb9a32) compiled @ Jul 1 2016 20:04:35
phy ver: 972, pp ver: 10.1

With this baudrate I'm not able to check the AT commands. Then, when I switch to a baudrate of 115200 I am able to communicate with the ESP:

Ai-Thinker Technology Co. Ltd.
ready
AT
OK
AT+CWL
ERROR
AT+CWJAP?
No AP
OK
AT+CWLAP?
ERROR
AT+CWLAP
+CWLAP:(4,"bbox2-7f0d",-88,"00:1 ",1,-46,0)
+CWLAP:(0,"PROXIMUS_FON",-94,"06: ec:6b",1,-47,0)
+CWLAP:(5,"PROXIMUS_AUTO_FON",-88,"0a: :ec:6b",1,-44,0)
+CWLAP:(3,"WiFi-2.4-BB3D-ext",-51,"00: 9a:38",1,-12,0)
+CWLAP:(3,"NGUYEN",-79,"e0:b ",11,-2,0)
+CWLAP:(0,"PROXIMUS_FON",-81,"42:6 ",11,0,0)
+CWLAP:(5,"PROXIMUS_AUTO_FON",-79,"42 ",11,0,0)
+CWLAP:(4,"WiFi-2.4-6858",-75,"4 e",11,1,0)
+CWLAP:(0,"PROXIMUS_FON",-89," ",11,-6,0)
OK

How is that possible that it has two different baudrates?

Thanks in advance,

Answer 1

How is that possible that it has two different baudrates?

Very simple. Exactly the same as the Arduino.

If you put:

Serial.begin(9600);

in your program then your sketch runs with the serial port at 9600 baud. However, just before then, the bootloader runs at 115200 baud for a few seconds listening for instructions from the PC.

There's no magic there.

You can even do it yourself:

Serial.begin(9600);
Serial.println("Hello at 9600 baud");
Serial.flush();
Serial.end();
Serial.begin(115200);
Serial.println("Hello at 115200 baud");
Serial.flush();
Serial.end();

The baud rate isn't fixed. It's whatever the firmware that is running at that precise moment deems it to be - whether that is the bootloader, the AT firmware, or your own custom sketch.